-lC 


^^>- 


SOUTHERN  REGIONAL  LIBRARY  FACIUTY  „g(J  JanUaFV  18,    190S. 


U.  S.  DEPA|       ilililPlililillllili       ^TURE, 

BUREAU  ^  A     001120  189     4  ,3^ 


A.  D.  MBl.VIN,  Chief  of  Bureau. 


FURTHER  EXPERIMENTS  CONCERNING  THE 

PRODUCTION  OF  IMMUNITY 

FROM  HOG  CHOLERA. 


BY 


M.  DORSFT.  M.  D.,  C  N.  MCBRYDE,  M.  D., 

AND 

W.  B.  NILES,  L).  V.  M., 

Of  the  Biochemic  Division. 


WASHINGTON: 
govi:rnmi:nt  I'KINti.ng  officU. 

I  "IIS 


1   r    "^rTi 


Digitized  by  the  Internet  Arciiive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


y  \ 


http://www.archive.org/details/furtherexperimenOOdorsiala 


Issued  January  18,  1908. 

U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ANIMAL  INDUSTRY.— BULLETIN   102. 
A.  D.  MELVIN,  Chief  of  Bureau. 


FURTHER  EXPERIMENTS  CONCERNING  THE 

PRODUCTION  OF  IMMUNITY 

FROM  HOG  CHOLERA. 


BY 


M.  DORSET.  M.  D.,  C.  N.  MCBRYDE,  M.  I)., 

AND 

W.  B.  NILES,  1).  V.  M., 

Of  the  Biochemic  Division . 


WASHINGTON: 

GOVHRNMHNT    I'RINTING    OFFICE. 
1 9  0  S  . 


THE  BUREAU  OF  ANIMAL  INDUSTRY. 

Chief:  A.  D.  Melvin. 
Assistant  Chief:  A.  M.  Faurington. 
Chief  Clerk:  E.  B.  Jones. 

Bioehemie  Division:  M.  Dorset,  chief;  James  A.  Emmery,  assistant  chief. 
Dairy  Division:  En.  II.  Webster,  chief;  C.  B.  Lane,  assistant  chief . 
Inspection  Division:  Rice  P.  Steddom,  chief;  Morris  Wooden,  R.  A.  Ramsay,  and 
Albert  E.  Behxke,  associate  chiefs. 

Pathological  Division:  John  R.  Mohler,  chief;  Henry  J.  Washburn,  assistant  chief. 

Quarantine  Division:  Richard  W.  Hickman,  chief. 

Division  of  Zoology:  B.  H.  Ransom,  chief. 

Experiment  Station:  E.  C.  Schroeder,  superintendent;  W.  E.  Cotton,  assistant. 

Animal  Husbandman:  George  M.  Rom.\iel. 

Editor:  James  M.  Pickens. 

lAbrarian:  Beatrice  Oberly  Rogers. 

Bioehemie  Division. 

Chief:  M.  Dorset. 

AssiMant  Chief:  James  A.  Emery. 

Meat  inspection  laboratories:  Central  laboratory,  T.  M.  Price  in  charge;  Philip  Cas- 
tleman,  E.  H.  Ingersoll,  F.  D.  Hardesty,  A.  V.  Fuller,  E.  J.  Ralph.  a.ssistants.  Chem- 
ists in  branch  laboratories:  Ralph  Hoagland,  A.  E.  Graham,  C.  H.  Swanger,  A.  H. 
Roop.  W.  B.  Smith,  E.  A.  Beyer,  Clarence  T.  N.  Marsh,  W.  P.  Colvin.  W.  C.  Powick. 

Hog  cholera  investigations:  In  charge  of  Chief  of  Division;  C.  N.  McBryde,  bacteri- 
ologist; W.  B.  Xiles,  inspector  in  charge  of  field  experiments;  Frank  W.  Tilley,  assist- 
ant bacteriologist. 

Bacteriological  investigations  of  meat  food  products:  C.  N.  McBryde,  bacteriologist,  in 
charge. 

Investigations  of  dips  and  disinfectants:  Robert  M.  Chapin,  chemist;  C.  N.  McBryde, 
bacteriologist;  A.  M.  West,  assistant  bacteriologist;  J.  B.  Munro.  assistant  chemist. 

Preparation  of  tuberculin  and  mallein:  In  charge  of  Chief  of  Division ;  A.  M.  West  and 
H.  J.  Shore,  assistant  bacteriologists;  ^^'.  S.  Stamper,  H.  S.  McAuley,  Roy  E.  Burnett, 
assistants. 

2 


LETTER  OF  TRANSMITTAL. 


U.  S.  Department  of  Agriculture, 

Bureau  of  Animal  Industry, 
Washington,  D.  C,  September  25,  1907. 
Sir:  I  have  the  honor  to  transmit  herewith  a  paper  entitled  "Fur- 
ther Experiments  Concerning  the  Production  of  Immunity  from 
Hog  Cholera,"  by  Doctors  M.  Dorset,  C.  N.  McBryde,  and  W.  B. 
Niles,  of  the  Biochemic  Division  of  this  Bureau,  and  to  recommend 
its  publication  as  a  bulletin  in  the  Bureau  series. 

This  paper  embodies  the  records  of  experiments  carried  out  during 
the  seasons  of  1903,  1904,  1905,  and  1906,  this  work  being  a  continua- 
tion of  that  reported  in  Bulletin  72  of  this  Bureau.  The  results 
obtained  show  quite  clearly  that  a  comparatively  certain  method  of 
protecting  hogs  from  hog  cholera  has  been  secured.  The  experiments, 
however,  have  not  as  yet  been  extensive  enough,  nor  have  they  been 
applied  under  the  varying  conditions  of  practice  to  a  sufficient  extent 
to  warrant  claims  concerning  the  practical  value  of  the  methods 
described  in  this  paper,  though  it  is  strongly  believed  that  they  should 
be  of  great  service  in  combating  hog  cholera  in  tliis  country. 
Very  respectfully,  " 

A.  D.  Melvin, 
Chief  of  Bureau. 
Hon.  James  Wilson, 

Secretary  of  Agriculture. 


CONTENTS. 


Page. 

Introduction 5 

Preliminary  experiments 7 

Experiments  of  1903  and  1904 7 

Experiments  of  1905 9 

Immunes  used  for  production  of  serum  in  1905 10 

Vaccination  experiments  in  1905 12 

Experiments  of  1906 17 

Plan  of  the  experiments 17 

General  plan  for  the  production  of  serum  in  190(5 18 

Description  of  the  Scribner  outbreak 20 

Scribner  immunes 20 

Description  of  the  Syphax  outbreak 23 

Syphax  immunes 24 

Vaccination  experiments  in  1900 27 

Tests  of  serum  from  hogs  hyperimmunized  with  blood  from  the  Scrib- 
ner outbreak 28 

Tests  of  serum  from  hogs  hyperimmunized  with  blood  from  the  Syphax 

outbreak 51 

Production  of  a  protectiye  serum  by  using  a  reduced  dose  of  diseased 

blood 68 

Experiments  with  serum  from  no«hyperimmunized  immunes 71 

Experiments  with  suckling  pigs 74 

Curative  value  of  hyperimmune  serum 81 

Duration  of  protective  power  in  blood  of  immunes,  and  keeping  quality  cf 

hyperimmune  serum 86 

General  summary  ofjesults 89 

Transmission  of  disease  by  hogs  treated  by  serum-simultaneous  method . .  90 

Immunity  in  hogs  after  serum-simultaneous  vaccination 91 

Immunity  in  hogs  treated  with  serum  alone 92 

Curative  value  of  hyperimmune  serum 92 

Results  with  serum  from  immunes  treated  by  different  methods  with  dif- 
ferent disease-producing  bloods 93 

Comparison  of  the  quick  and  slow  methods  of  producing  hyperimmune 

serum 93 

The  comparative   potency  of  sera    secured    by  hyperimmunization 

with  the  Scribner  and  Syphax  strains  of  disease 93 

Comparative  potency  of  sera  from  hogs  possessing  natural  immunity 

and  from  those  possessing  acquired  immunity 94 

Conclusions 95 

4 


FURTHER  EXPERIMENTS  CONCERNING  THE  PRODUC- 
TION OF  IMMUNITY  FROM  HOG  CHOLERA. 


INTRODUCTION. 

In  a  previous  publication  from  this  Bureau"  it  has  been  shown 
that  the  disease  knowTi  as  hog  cholera,  encountered  in  epizootic  form 
in  Iowa  and  other  parts  of  the  United  States,  is  caused  by  a  filterable 
and  probably  ultramicroscopic  virus  which  exists  in  the  blood  of  sick 
hogs,  and  that  Bacillus  cholerse  suis,  although  present  in  most  cases  of 
hog  cholera,  in  all  likelihood  plays  the  part  of  a  secondarj'  invader. 
This  modification  of  our  views  regarding  the  etiology  of  hog  cholera 
necessarily  carried  with  it  changes  in  plans  for  combating  the  disease. 

Most  of  the  methods  for  combating  the  disease  wliich  have  hereto- 
fore been  proposed  were  very  naturally  based  upon  the  general  belief 
that  B.  cholerse  suis  was  the  cause  of  hog  cholera,  and  many  different 
methods  of  preparing  vaccines  and  antitoxic  sera  through  the  use  of 
that  organism  were  devised  and  subjected  to  extensive  laboratory  as 
well  as  practical  tests.  Although  a  certain  degree  of  success  was  appar- 
ently attained  in  some  instances,  none  of  these  methods  have  been 
found  to  act  with  sufficient  reliability  to  warrant  their  use  in  practice. 

In  the  case  of  vaccines  prepared  from  cultures  of  B.  cholerse  suis  a 
certain  amount  of  immunity  against  that  organism  may  have  been 
at  times  induced  in  the  treated  hogs,  and  a  similar  result  may  have 
been  secured  by  the  administration  of  antitoxins  jirepared  through 
the  use  of  the  same  organism,  for  in  the  earlier  publication  above 
referred  to  it  has  been  shown  that  B.  cholerse  suis  usually  invades  the 
body  of  the  hog  after  injection  with  the  filteral)le  virus,  autl,  as 
stated  there,  it  is  reasonable  to  believe  that  the  final  result  of  the 
disea.se  is  in  many  causes  materially  influenced  by  the  ])rosence  of  tiiat 
organism.  Any  vaccine  or  .senim  which  protects  against  B.  cholene 
suis  would  therefore  be  expected  to  aid  the  body  in  its  struggle 
against  the  twofold  invasion  of  filteral)le  virus  and  /^  chohnc  suis. 
We  believe  tiiat  the  partial  .success  attained  at  tim(>s  l)y  the  use  of 
sera  and  vaccines  prepared  from  B.  cholenr  suis  is  to  i)e  explained 
upon  this  ground. 

In  view  of  the  fact,  however,  that  the  filterable  virus  is  the  ])riniarv 
invader,  and  that  it  appears  to  be  quite  .sufficient  in  itself  to  cau.se 

o  Uullctin  72,  Buroau  of  .Vnimal  Indu.stry,  l'.  S.  Dt-pt.  of  Agrioillun'. 

5 


6  PBODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 

the  death  of  most  hogs,  any  substance  which  protects  only  from  B. 
cholerse  suis  must  necessarily  be  regarded  simply  as  a  palliative,  which, 
in  the  light  of  past  experiences,  is  \vithout  a  value  that  is  in  any  way 
commensurate  with  the  cost  of  applying  it. 

It  thus  seems  evident  that  all  efforts  looking  to  the  prevention  or 
treatment  of  hog  cholera  should  be  directed  primarily  toward  secur- 
ing some  means  of  protecting  the  hog  from  invasion  by  the  filterable 
virus,  or  of  overcoming  that  virus  if  invasion  has  already  taken  place. 

Since  it  was  first  definitely  determined  that  B.  cholerx  suis  is  not 
the  primary  cause  of  hog  cholera  the  work  of  the  Bureau  of  Animal 
Industry  has  been  along  the  lines  just  suggested.  Much  difficulty 
has  been  experienced  in  carrying  out  this  work,  due  in  great  measure 
to  our  inability  to  cultivate  the  filterable  virus  artificially  and  to  the 
fact  that  of  all  animals  exposed  to  this  virus  only  hogs  have  proven 
susceptible.  We  have  thus  been  restricted  to  the  use  of  the  blood 
and  tissues  of  sick  hogs  in  our  attempt  to  secure  a  satisfactory  serum 
or  vaccine. 

As  stated  in  Circular  43  of  this  Bureau,  issued  February  12,  1904, 
"  the  basis  of  the  immunity  experiments,  therefore,  has  been  the  use 
of  attenuated  and  disease-producing  liquid  or  dried  blood,  or  the  use 
of  this  blood  mixed  with  blood  obtained  from  immune  animals,  in 
which  animals  the  immunity  has  been  increased  by  the  injection  of 
large  doses  of  disease-producing  blood  obtained  from  hogs  known  to 
have  the  disease;  or,  in  other  words,  disease-producing  blood  and  anti- 
toxic blood  separate  and  combined  have  been  successfully  used."  ° 

The  efforts  to  attenuate  the  virus  in  blood  from  diseased  hogs  by 
dr}"ing,  by  heat,  and  by  chemical  agents  have  not  led  to  satisfactory 
results.  This  appears  to  be  due  in  part  at  least  to  the  unequal 
resistance  of  the  virus  in  different  lots  of  diseased  blood  to  these 
agencies.  At  times  the  protection*  afforded  by  diseased  blood 
attenuated  artificially  has  appeared  to  be  complete;  at  others  a 
vaccine  prepared  in  identically  the  same  manner  has  either  caused 
death,  thus  showing  an  entire  lack  of  attenuation,  or  else  the  hogs 
have  shown  no  ill  effects  from  the  vaccination  but  have  succumbed 
promptly  when  exposed  to  hog  cholera,  showing  that  the  supposed 
vaccine  had  no  protective  power  whatever. 

It  may  be  that  later  investigations  will  show  that  it  is  possible  to 
obtain  a  satisfactory  vaccine  for  hog  cholera  by  attenuating  the  virus, 
but  our  own  results  were  so  discouraging  that  efforts  in  this  direction 
were  abandoned  and  our  entire  attention  turned  to  the  production  of 
a  serum  in  the  manner  hereinafter  described. 

o  Subsequent  to  the  publication  of  Circular  43,  Boxmeyer  and  McClintock  (Journal 
of  Infectious  Diseases,  vol.  2,  No.  2,  March,  1905),  described  a  few  experiments  along 
these  lines  and  scerae<l  to  obtain  better  results  by  using  a  combination  of  disease- 
producing  blof)d  and  immune  serum  than  by  using  an  artificially  attenuated  virus. 


RESULTS    OF    EARLY    EXPERIMENTS.  7 

PRELIMINAEY   EXPERIMENTS. 

The  earlier  experiments,  which  had  for  their  object  the  production 
of  a  serum  which  would  protect  from  the  filterable  virus,  were  not 
wholly  successful,  some  of  them  indeed  resulting  in  almost  complete 
failure;  but  as  these  failures  are  quite  instructive  on  account  of  the 
light  they  throw  upon  the  details  of  producing  the  serum,  it  seems 
desirable  to  describe  them  very  briefly  before  taking  up  the  more 
recent  work. 

As  it  was  known  that  immune  hogs  could  A\athstand  perfectly 
injections  of  disease-producing  blood «  which  were  more  than  suffi- 
cient to  destroy  nonimmunes,  the  plan  originally  adopted  was  to 
inject  hogs  immune  from  hog  cholera  with  disease-producing  blood 
in  increasing  doses,  the  object  of  tliis  treatment  being,  of  course,  to 
impart  a  protective  power  to  the  blood  of  the  immune,  previous 
experiments  having  shown  that  blood  from  nonhyperimmunized 
immunes  possessed  very  little  if  any  such  power.  The  records  of  two 
experiments  carried  out  with  serum  from  immune  hog  844  treated  in 
this  manner  are  given  below. 

EXPERIMENTS   OF    1903   AND    1904. 

Immune  hog  844  was  an  adult  aninuil  weighing  approximately  150 
pounds,  which  had  recovered  from  an  attack  of  hog  cholera.  This 
immune  was  injected  subcutaneoush'  with  increasing  doses  of 
disease-producing  blood  which  had  been  shown  to  contain  the 
filterable  virus.'' 

The  amount  of  disease-producing  blood  injected  was  increased  to 
400  c.  c.  before  blood  was  drawn  from  the  immune. 

The  following  statement  shows  the  dates  and  amounts  of  disease- 
producing  blood  used  for  injection  of  imnmne  hog  844,*^  with  records 
of  blood   drawings: 

July  24,  1903,  1  c.  c.  (Ii.'<caso-prtxhiring  lilood  injected. 
Augu.st  4.  1903,  4  c.  c.  disea.'se-prodiuing  blood  injeeled. 
August  19,  1903,  12  e.  c.  dLsease-prodiicing  t)lood  injected. 
September  1.  1903,  .30  c.  c.  disea.'^e-producing  bl(H)d  injected. 
September  20,  1903,  .50  c  c.  disea-se-producing  l)lcx)d  injected. 
October  14,  1903,  250  c.  c  di-sea-se-producing  l)l(K)d  injected. 
October  20,  1903,  2.50  c.  c  di.sease-i)rodu<ing  Idood  injected. 
October  29,  1903,  400  c.  c  (H.-^eiU-c-iiroduciiig  l)l(M)d  injected. 
November  9,  1903,  1(X)  c.  c.  l)liM)d  drawn  licni  tail. 


"The  term  ''disea-xe-jiroducing  blood"  is  applied  in  this  j)ap«'r  to  bl<M)d  from  lioga 
affected  with  hog  cholera,  which  blood  wa.^  sliown  to  be  capal)l<'  of  causing  tlie  diseai^e 
when  injected  into  nonimmune  hogs. 

f*  See  experiment.s  with  blcnxl  from  Herd  I.  I>ulhtin  7J.  Uurcau  of  Animal  Industry, 
pp.  43-()5. 

f  We  acknowledge  our  indebtedne.>*.><  to  Dr.  K.  C  Schroc(b'r.  who  hiwlthcsc  injections, 
a«  well  a."*  those  de!<crib«Hl  under  experiments  A  and  H.  nuuie  for  us  at  liu'  Experiment 
Station  of  this  bureau  at  Itethe.sda.  Md. 


8  PRODUCTION    OF   IMMUNITY   FROM    HOG   CHOLERA. 

November  19,  1903,  400  o.  c.  disease-producing  blood  injected. 
December  10,  1903,  480  c.  c.  disea.^e-producing  blood  injected. 
January  4.  1904,  150  c.  c.  blood  drawn  from  tail. 
January  5,  1904,  490  c.  c.  disease-producing  blood  injected. 
January  28,  1904,  480  c.  c.  disease-producing  blood  injected. 
February  9,  1904,  185  c.  c.  blood  drawn  fR)m  tail. 

It  is  interesting  to  note  that  even  the  largest  doses  of  disease- 
producing  blood  did  not  seriously  disturb  the  general  health  of  the 
immune,  the  only  ill  effects  noted  after  the  injection  of  the  blood 
being  swelling  at  the  point  of  injection  and  occasionally  a  temporary 
loss  of  appetite. 

Two  experiments  to  test  the  protective  value  of  the  blood  drawn 
from  hog  844  were  carried  out. 
Table  1. — Experiment  A  with  blood  drawn  November  9,-1903,  from  irnmune  hog  844. 


No.  of 

Material  injected. 

Inoculation. 

Exposure. 

hog. 

Date. 

Resiilt. 

Date. 

Result. 

1002. . . . 
1004 

20  c.  c.  defibrinated  blood  of   hog  844, 

subcutaneously . 
20  c.  c.  defibrinated  blood  of  hog844-H 

1  c.c.  disease-producing  blood. 

Nov.  11, 1903 
do 

Remained 

well. 
do 

Dec.   18,1903 
do 

Died;   hog 
cholera. 

1003 

.   ..do 

Died;  hog 
cholera. 

well. 

■ 

Table  2. — Experiment  B  with  blood  drawn  February  9,  1904,  from  immune 

hog  844. 

No.  of 

Material  injected. 

Inoculation. 

Exposure. 

hog. 

Date. 

Result. 

Date.             Result. 

1086. . . . 
1087     . 

20c. c. blood  of  hog 844+1  c.c. disease- 
producing  blood. 
do 

Feb.   11,1904 
do 

Remained 

well. 
do 

Mar.  11,1904 
do 

Died;  hog 
cholera. 

1088 

do 

do 

do 

do 

well. 

1089 

.do      

do. 

...do 

do 

covered . 

Died;   hog 

cholera. 

1090     .. 

1  c.  c.  disease-producing  blood  alone . . . 
do 

do 

do 

Died;  hog 

cholera. 

do 

1091 

Experiment  A. — By  referring  to  Table  1  it  will  be  seen  that  only 
three  hogs  were  used  in  this  experiment.  Of  these,  after  injection, 
the  one  that  received  only  immune  blood  remained  well;  the  one 
which  received  both  immune  blood  and  disease-producing  blood 
also  remained  well,  while  the  third  animal  which  received  only  dis- 
ease-producing blood  died  of  hog  cholera.  When  the  two  surviving 
hogs  were  injected  approximately  thirty  days  later  with  disease- 
producing  blood  to  test  their  immunity  the  one  wliich  had  been 
treated  previously  with  immune  blood  alone  died,  while  the  other 
which  had  received  the  mixture  of  immime  blood  and  disease-pro- 
ducing blood  remained  well. 

Experiment  B.  — This  experiment  was  designed  as  a  control  on  the 
results  of  experiment  A,  except  that  it  was  considered  unnecessary  to 
use  the  immune  serum  alone,  as  it  appeared  not  to  produce  any 


METHODS    OF    HYPERIMMUNIZING    HOGS.  9 

lasting  immimity.  One  point  of  difference  between  experiments  A 
and  B  should  be  noted :  Experiment  B  was  carried  out  with  immime 
blood  drawn  February  9,  1904,  whereas  in  experiment  A  the  drawing 
of  November  9,    1903,  was  used. 

The  two  experiments  agree  in  showing  that  the  serum  from  the 
hyperimmunized  immune  was  capable  of  protecting  hogs  from  hog 
cholera  when  the  infection  took  place  simultaneously  with  the 
administration  of  the  immune  serum.  It  is  evident,  however,  that 
the  duration  of  the  immunity  secured  by  these  injections  was  not 
of  sufficient  length  to  render  the  method,  as  used  at  that  time,  suit- 
able for  practical  purposes.  Other  experiments  with  blood  from 
immune  hog  844  and  from  other  hyperimmunized  hogs  about  the 
same  time  did  not  lead  to  more  promising  results,  and  the  experi- 
ments were  therefore  laid  aside  temporarily  on  account  of  the  pressure 
of  other  work. 

EXPERIMENTS  OF  1905. 

In  the  spring  of  1905  this  work  was  resumed  with  the  intention  of 
determining  whether  it  was  possible  to  secure  by  means  of  the  above- 
described  method,  or  some  variation  of  it,  an  immunity  which 
would  be  more  lasting  than  that  obtained  in  previous  experiments. 

Four  immunes  were  used  to  supply  serum.  These  hogs  were  all 
adult  animals,  more  than  a  year  old,  and  had  all  passed  tlu'ough 
exposure  to  hog  cholera  without  exliibiting  noticeable  symptoms 
of  disease.  It  is  difficult  to  classify  these  hogs  as  possessing  either 
"natural"  immunity  or  "acquired"  immunity,  as  they  may  have 
suffered  a  light  attack  of  disease  which  passed  by  unnoticed.  It  is 
quite  certain,  however,  that  they  possessed  considerably  greater 
powers  of  resistance  than  is  ordinarily  the  rule  in  hogs. 

Two  methods  were  resorted  to  for  lu'perimniunizing  these  hogs. 
For  the  sake  of  convenience  the  fu^st  plan  lias  been  designated  the 
"slow  method"  and  the  second  the  "quick  method,"  depending 
upon  the  manner  of  injecting  the  disease-producing  blood.  The 
sfow  method  consisted  of  three  successive  injections  of  disease- 
producing  blood,  followed  by  a  drawing  of  blood  from  the  immune, 
and  then  more  injections  of  disease-producing  blood,  followed  by 
more  drawings  from  the  inmiune;  in  other  words,  it  followed  in  a 
general  way  the  plan  used  in  raising  the  potency  of  the  blood  serum 
of  immune  cattle  for  securing  a  protective  serum  for  "rinderpest." 
The  quick  method  is  along  the  line  of  Xioolle's  so-called  "ni^thode 
brutale"  of  producing  an  antirinderpest  serum,  and  was  planned  to 
consist  of  one  very  large  dose  of  disease-producing  blood  administered 
subcutaneously,  and  followed  after  an  inters'al  of  ten  days  or  more 
by  l)lo()(l  drawings  from  the  immune.  It  was  planned  to  u.se  a 
different  strain  of  disease-producing  blood  for  injecting  each  immune, 
but  this  could  not  be  done  owing  to  the  impossibility  of  securing  a 


10  PRODUCTION   OF   IMMUNITY   FEOM   HOG  CHOLERA. 

suflBcient  quantity  of  blood  from  different  outbreaks  at  the  time 
the  injections  were  to  be  made.  All  of  the  immunes,  therefore,  were 
injected  with  diseased  blood  which  might  be  considered  a  mixture 
of  several  different  strains,  but  which  was  virulent  in  all  cases  (as 
proven  by  the  injection  of  controls)  unless  otherwise  stated. 

In  view  of  the  virulence  of  this  blood  the  behavior  of  the  immunes 
after  injection  seems  truly  remarkable,  for  not  one  of  them  showed 
any  ill  effects  whatever  other  than  a  transitory  stiffness,  due  undoubt- 
edly to  the  local  inflammation  caused  by  the  large  injections.  Immune 
hog  Q  No.  2  received  1,440  times  the  usual  lethal  dose  of  hog-cholera 
blood  without  any  effect  whatever  being  noticeable  except  a  little 
stiffness.  As  far  as  the  immune  is  concerned,  therefore,  there 
seemed  to  be  no  reason  why  the  single  large  dose  should  not  be  used 
instead  of  the  much  slower  process  of  administering  the  disease- 
producing  blood  in  increasing  doses. 

nvnvrUTTES  used  for  production  of  SERXJM  in  1906. 

A  very  brief  history  of  each  of  the  immunes  is  given  below.  It 
should  be  noted  that  the  virulence  of  the  disease-producing  blood 
injected  was  tested  each  time  by  the  injection  of  one  or  more  non- 
immune hogs,  and  in  each  case  it  proved  to  be  of  high  pathogenic 
power  unless  otherwise  stated. 

Hyperimmunized  Immune  Q  No.  1  (Quick  Method). 

This  hog  passed  through  an  exposure  to  hog  cholera  in  the  summer 
of  1904  without  showing  any  symptoms  of  disease,  and  was  not  sub- 
jected to  further  exposure  until  the  summer  of  1905,  when  it  weighed 
approximately  130  pounds.  On  September  12,  1905,  it  was  injected 
subcutaneously  with  900  c.  c.  of  blood  that  was  supposed  to  be  viru- 
lent, but  nonimmune  hogs  that  were  given  small  doses  of  the  same 
blood  did  not  sicken,  so  the  treatment  had  to  be  repeated.  On 
October  16,  1905,  this  hog  was  given  1,275  c.  c.  of  virulent  blood. 
No  reaction  worthy  of  note  followed  this  injection.  Blood  draw- 
ings from  this  immune  were  made  as  follows : 

November  1,  1905,  140  c.  c.  defibrinated  blood  obtained. 
November  9,  1905,  125  c.  c.  defibrinated  blood  obtained. 
November  16,  1905,  150  c.  c.  defibrinated  blood  obtained. 
December  27,  1905,  200  c.  c.  defibrinated  blood  obtained. 

The  first  drawing  of  this  blood  was  used  in  the  vaccination  of  hogs 
in  the  1905  experiment. 

Hyperimmunized  Immune  Q  No.  2  (Quick  Method). 

This  hog  passed  through  an  exposure  to  hog  cholera  in  1904  with- 
out showing  any  symptoms  of  disease.  On  November  1,  1905, 
when  the  hog  weighed  145  pounds,  it  was  injected  subcutaneously 
with  1,440  c.  c.  of  disease-producing  blood.  Some  soreness  and 
stiffness  followed  this  injection,  but  otherwise  the  animal  remained 
well. 


IMMUNES    USED    FOR   PRODUCTION    OF    SERUM.  11 

Drawings  of  blood  were  made  from  hog  Q  No.  2  as  follows: 

November  24,  1905,  225  c.  c.  of  defibrinated  blood  obtained. 
December  1,  1905,  230  c.  c.  of  defibrinated  blood  obtained. 
December  8,  1905,  200  c.  c.  of  defibrinated  blood  obtained. 
December  27,  1905,  350  c.  c.  of  defibrinated  l)lood  obtained. 

The  first  drawing  of  blood  from  this  hog  was  used  in  the  vaccination 
of  hogs  in  the  1905  experiments,  and  the  second  drawing  was  used  in 
the  1906  experiment  to  test  the  keeping  quality  of  immune  serum. 

Hyperimmuxizeu  Immune  1234  (Slow  Method). 

This  hog  was  first  exposed  to  hog  cholera  on  November  9,  1904, 
when  it  was  placed  in  a  pen  with  sick  hogs;  no  illness  resulted.  On 
September  29,  1905,  at  which  time  it  weighed  168  pounds,  hog  1234 
was  injected  subcutaneously  with  175  c.  c.  of  disease-producing 
blood.  This  was  followed  on  October  21  by  420  c.  c.  of  disease-pro- 
ducing blood,  and  the  third  dose,  840  c.  c,  was  given  November  5, 
1905.  About  two  months  later,  or,  to  be  exact,  on  January  13,  1906, 
the  hog  received  the  last  dose  of  disease-producing  blood.  The 
vindence  of  the  blood  used  for  each  of  these  injections  was  proven  by 
the  production  of  disease  in  nonimmune  hogs.  Drawings  of  blood 
were  made  from  the  tail  of  this  hog  as  follows : 

November  14,  1905,  100  c.  c.  defibrinated  blood  obtained. 
November  21,  1905,  130  c.  c.  defibrinated  blood  obtained. 
November  28,  1905,  125  c.  c.  defibrinated  bl(X)d  obtained. 
January  24,  190G,  450  c.  c.  defibrinated  blood  obtained. 
February  2,  1905,  525  c.  c.  defibrinated  blood  obtained. 
August  31,  1906,  60  c.  c.  defibrinated  blood  obtained. 

The  first  drawing  of  serum  from  hog  1234  was  used  in  the  1905 
experiments,  while  the  second  dra\\ing  and  last  drawing  were  used 
in  1906  Experiments  XXVIII  and  XXIX,  hereinafter  described. 

Hyperimmunized  Immune  1212  (Slow  Method^ 

Hog  1212  was  injected  with  blood  from  a  sick  hog  on  August  27, 
1904,  and  was  later  placed  in  the  exposure  pen,  but  in  neither  instance 
did  the  hog  become  sick. 

On  September  29,  1905,  tliis  immune  weighed  approximately  160 
pounds  and  was  injected  with  175  c.  c.  of  disease-producing  blood. 
The  injection  of  disease-producing  blood  was  repeated  as  follows: 

October  21,  1905,  420  r.  c. 
November  5,  1905,  820  c.  c. 
January-  13.  1906.  840  c.  c. 

Practically  no  .symptoms  followed  these  injections,  although  non- 
immimes  that  received  only  5  c.  r.  of  the  same  blood  contracted  hog 
cholera  and  in  most  instances  died. 


12  PRODUCTION   OF   IMMUNITY  FROM    HOG  CHOLERA. 

Drawings  of  blood  were  made  from  immune  hog  1212  as  follows: 

November  14,  1905,  100  c.  c.  defibrinated  blood  obtained. 
November  21,  1905,  140  c.  c.  defibrinated  blood  obtained. 
November  28,  1905,  10  c.  c.  defibrinated  blood  obtained. 
January  24,  1906,  75  c.  c.  defibrinated  blood  obtained. 

The  first  drawing  of  this  serum  was  the  only  one  used  for  experi- 
mental purposes,  and  this  was  used  in  the  1905  experiments  only. 

VACCINATION  EXPERIMENTS  IN  1906. 

Only  the  first  drawings  of  hyperimmune  blood  were  used  in  the 
experiments  described  below.  The  blood  was  defibrinated,  separated 
from  the  clot,  and  mixed  with  sufficient  5  per  cent  carbolic  acid  solu- 
tion to  give  a  0.5  per  cent  solution  in  the  defibrinated  blood. 

In  so  far  as  the  method  of  vaccination  is  concerned,  the  1905  exper- 
iments practically  repeat  those  of  1903  and  1904,  though  of  course 
the  mode  of  hyperimmunizing  the  immunes  was  modified  as  ex- 
plained above.  It  was  also  hoped  to  determine  whether  different 
immunes  varied  in  their  power  to  yield  a  potent  serum,  whether  the 
"quick"  or  the  "slow"  method  of  hyperimmunization  was  prefer- 
able, and  whether  by  increasing  the  amount  of  disease-producing 
blood  given  to  the  immunes  the  duration  of  the  immunity  in  treated 
hogs  could  be  prolonged.  The  amount  of  disease-producing  blood 
administered  wdth  the  immune  blood  for  the  purposes  of  vaccination 
was  also  varied  for  similar  reasons.  In  all  treated  hogs  the  diseased 
blood  and  the  hyperimmune  serum  were  injected  simultaneously  on 
different  sides  of  the  body  beneath  the  skin.  Control  animals  of  the 
same  size  and  age,  and  of  the  same  litters  also,  if  available,  were  in- 
jected with  the  same  dose  of  the  same  disease-producing  blood  alone 
in  order  to  demonstrate  the  protective  value  of  the  immune  blood. 

Several  weeks  after  vaccination  the  hogs  which  withstood  the  treat- 
ment were  placed  in  an  "exposure  pen.""  This  pen  contained  hogs 
sick  of  hog  cholera,  and  as  the  pen  was  comparatively  small  the  ex- 
posure to  which  the  treated  hogs  were  subjected  was  quite  as  severe 
as  any  that  could  be  encountered  under  natural  conditions  by  asso- 
ciation. The  severity  of  this  exposure  is  made  plain  by  the  death  of 
the  control  animals. 

It  seems  unnecessary  to  give  detailed  records  of  the  hogs  used  in 
this  and  succeeding  experiments.  It  may  be  stated,  however,  that  in 
cases  where  hogs  became  sick  the  clinical  records  and  the  autopsy 
findings  in  all  cases  were  such  as  are  usually  met  with  in  hog  cholera, 
unless  otherwise  stated.     The  salient  features  are  set  down  in  Table  3. 

"  The  term  "exposure  pen  "  as  used  in  this  paper  refers  to  a  pen  where  hogs  sick  of  hog 
cholera  were  kept  and  hogs  placed  therein  were  subjected  at  all  times  to  close  associa- 
tion with  the  sick  animals.  The  exposure  was  entirely  by  association,  as  the  hogs  were 
not  allowed  to  feed  upon  the  bodies  of  those  that  died. 


RE8ULTS    OF   VACCINATIONS    IN   1905    EXPERIMENTS. 


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PRODUCTION    OF   IMMUNITY   FROM    HOG   CHOLERA. 


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As  will  be  seen  from 
Table  3,  16  hogs  were 
vaccinated  by  the  use  of 
a  combination  of  hyper- 
immune blood  and  dis- 
ease-producing blood, 
blood  from  each  immune 
serving  for  the  treatment 
of  4  hogs  in  doses  of  10 
c.  c.  and  20  c.  c.  Half 
of  the  treated  hogs  re- 
ceived 2  c.  c.  of  disease- 
producing  blood  and  the 
remainder  1  c.  c,  simul- 
taneously with  the  im- 
mune blood.  For  the 
purpose  of  control,  8 
hogs  were  injected  with 
disease-producing  blood 
alone,  half  of  these  re- 
ceiving 2  c.  c.  and  the 
remainder  1  c.  c,  all 
injections  being  made 
subcutaneously. 

Of  the  16  hogs  which 
were  vaccinated,  2  died, 
2  became  sick  but  re- 
covered, and  12  showed 
no  symptoms  of  illness 
whatever  as  a  result  of 
the  treatment.  The  ani- 
mals which  became  sick 
were  all  treated  with  se- 
rum from  immune  hog 
Q  No.  1,  the  serum  from 
this  immune  appearing 
to  be  barely  sufficient  to 
protect  from  1  c.  c.  of 
disease-producing  blood, 
but  not  potent  enough 
to  protect  from  2  c.  c. 
Serum  from  the  other  3 
immunes  gave  perfect 
protection  from  2  c.  c. 
as  well  as  from  1  c.  c.  of 


DEGEEE    OF   IMMUNITY    FROM   VACCINATION.  15 

disease-producing  blood  when  injected  simultaneously  with  it,  and  the 
protection  afforded  by  10  c.  c,  of  this  serum  seemed  to  be  quite  as 
satisfactory  as  that  secured  by  the  use  of  twice  that  amount. 

The  protective  power  of  the  serum  from  hyperimmunized  hogs  Q 
No.  2,  1234,  and  1212  is  made  strikingly  apparent  by  the  behavior 
of  the  control  animals,  which  were  injected  with  disease-producing 
blood  alone.  Of  the  8  hogs  thus  injected,  6  died  of  hog  cholera,  1 
was  killed  when  in  a  moribund  condition,  and  the  eighth  hog  also 
contracted  the  disease  but  recovered.  From  these  facts  there  seems 
to  be  no  reason  for  doubting  the  protective  power  of  the  serum  from 
these  3  immunes  when  injected  simultaneously  with  disease-produc- 
ing blood. 

In  order  to  determine  whether  or  not  this  immunity  was  of  more 
than  fleeting  duration  the  survivors  from  the  vaccinating  dose  were 
placed  in  the  exposure  pen  together  with  7  untreated  healthy  hogs, 
as  shown  in  Table  3.  This  exposure  to  disease  by  association  took 
place  twenty-four  days  after  vaccination  in  the  case  of  6  of  the 
treated  hogs  and  twenty-five  days  after  the  vaccination  of  the 
remaining  8  hogs.  The  interval  between  vaccination  and  exposure 
was  not  as  long  as  was  desired,  but  owing  to  the  lateness  of  the  season 
it  was  considered  best  to  expose  at  that  time  rather  than  wait  until 
the  following  summer. 

It  will  be  seen  from  the  table  that  not  one  of  the  vaccinated  hogs 
contracted  disease  as  a  result  of  this  exposure.  Of  the  7  control  hogs 
which  were  placed  in  the  exposure  pen  at  the  same  time  as  the  vacci- 
nated hogs  to  prove  the  virulence  of  the  exposure,  5  contracted  hog 
cholera,  while  2  remained  well.  Of  the  5  which  contracted  the  dis- 
ease, 3  died  and  2  were  killed  when  desperately  sick  to  secure  blood 
for  other  experiments. 

From  the  results  given  above  there  seems  to  be  no  reason  to  doubt 
the  power  of  serum  from  hyperimmunized  immunes  to  protect  non- 
immunes from  a  fatal  dose  of  disease-producing  blood  administered 
simultaneously  with  the  hyperimmune  serum.  It  appears  also  that 
in  the  case  of  serum  from  3  of  the  immunes,  at  least,  a  dose  of  10  c.  c. 
was  quite  as  effective  as  20  c.  c.  The  serum  from  both  immunes 
which  were  hyperimmunized  by  the  slow  method  proved  potent, 
whereas  serum  from  immune  hog  Q  No.  1  treated  by  the  quick  method 
failed  to  give  satisfactory  results.  The  low  protective  power  of  the 
serum  from  this  immune  would  appear  to  be  due  to  some  peculiarity 
on  the  part  of  the  immune  itself,  inasmuch  as  blood  from  immune  hog 
Q  No.  2  treated  by  the  same  method  proved  quite  as  effective  as  blood 
from  either  of  the  "slow"  immimes.  Without  more  extended  trials, 
therefore,  with  other  immunes,  preference  could  not  be  given  to  either 
one  of  the  method.s  of  hypcriinmimization  over  the  other.  These 
experiments  indicate  also  that  large  doses  of  disease-producing  blood 


16  PRODUCTION   OF    IMMUNITY   FROM    HOG    CHOLERA. 

may  be  expected  to  confer  upon  the  blood  of  the  immune  the  power 
to  protect  nonimmunes  for  a  greater  length  of  time  than  blood  from 
immunes  which  receive  considerably  smaller  doses,  for  in  the  experi- 
ments carried  out  up  to  this  time  the  immunity  exhibited  by  the 
vaccinated  hogs  after  treatment  may  have  been  due  (in  some  of  the 
treated  hogs  at  least)  to  the  action  of  the  immune  blood  alone  and 
not  necessarily  to  the  combined  action  of  immune  and  disease-pro- 
ducing blood. 

It  will  be  remembered  that  in  the  experiments  of  1903  and  1904 
the  immune  blood  protected  the  treated  animals  from  the  disease- 
producing  blood  which  was  administered  simultaneously  with  it,  but 
some  of  the  vaccinated  animals  succumbed  when  exposed  to  hog 
cholera  about  thirty  days  later.  The  most  rational  explanation  of 
this  occurrence  appeared  to  lie  in  the  supposition  that  too  much 
immune  blood  was  administered  with  the  diseased  blood.  The 
animals  would  thus  be  completely  protected  from  the  simultaneous 
injection  of  the  virus,  but  owing  to  this  complete  protection  from  the 
virus  the  animal  body  would  have.no  stimulus  to  bring  about  a  reac- 
tion and  a  consequent  production  of  an  active  immunity  which  was 
aimed  at  by  the  simultaneous  method  of  vaccination.  Under  such 
circumstances  it  seemed  reasonable  to  suppose  that  the  vaccinated 
hogs  possessed  only  a  passive  and  transitory  immunity,  such  as  might 
be  expected  from  the  injection  of  an  antitoxin. 

In  the  experiments  of  1905  we  were  unable  to  clear  up  this  point, 
owing  to  difficulties  experienced  in  securing  suitable  material  for  the 
work.  The  experiments  were  greatly  delayed  and  it  was  only 
possible  to  carry  out  those  which  have  just  been  described.  Inas- 
much as  no  hogs  were  injected  with  the  immune  serum  alone  in 
these  experiments,  the  question  as  to  the  nature  of  the  immunity 
afforded  by  our  injections  could  not  be  definitely  determined.  There 
is  reason  to  believe,  however,  that  this  may  have  been  due  to  the 
serum  alone,  at  least  in  the  case  of  those  which  received  20  c.  c.  of 
immune  serum,  while  there  can  be  no  doubt  that  the  2  hogs  1397  and 
1398,  which  became  sick  but  recovered,  secured  an  active  immunity. 
It  is  entirely  possible  that  the  other  hogs  which  received  10  c.  c.  of 
immune  blood  with  the  disease-producing  blood  suffered  a  very  mild 
attack  of  disease  and  thus  secured  an  active,  permanent  immunity. 
It  would  be  natural  to  suppose,  however,  that  if  10  c.  c.  of  immune 
serum  gave  sufficient  protection  from  the  disease-producing  blood  to 
prevent  any  outward  manifestation  of  disease  the  protection  afforded 
by  20  c.  c.  would  be  complete,  and  that  subsequent  immunity  in 
these  hogs  would  presumably  be  due  to  the  immune  blood  alone. 


DESCRIPTION    OF   THE    EXPERIMENTS    OF    1906.  17 

EXPERIMENTS  OF    1906. 

The  experiments  thus  far  described  show  quite  cleariy  that  blood 
from  certain  hyperimmunized  immunes  possesses  the  power  to  pro- 
tect nonimmune  hogs  from  a  fatal  dose  of  disease-producing  blood 
administered  simultaneously  with  the  serum.  It  has  also  been 
shown  that  hogs  which  survive  a  simultaneous  injection  of  serum  and 
disease-producing  blood  are  rendered  immune  for  at  least  twenty-five 
days  thereafter,  even  though  they  show  no  reaction  after  the  injection. 
Notwithstanding  the  success  which  attended  most  of  these  experi- 
ments, many  questions  affecting  the  practicability  of  this  method  for 
combating  hog  cholera  yet  remained  undetermined.  In  conducting 
the  experiments  during  the  year  1906,  therefore,  we  have  endeavored 
to  decide,  in  so  far  as  time  and  material  would  permit,  these  other 
questions  in  connection  with  experiments  designed  to  substantiate 
the  results  already  obtained. 

PLAN  OF  THE  EXPERIMENTS. 

The  experiments  which  are  to  be  described  hereafter  will  perhaps  be 
best  understood  by  indicating  the  general  plan  which  was  followed. 
The  questions  to  be  decided  concerned  first,  the  immunes,  and  second, 
the  hogs  that  were  to  be  vaccinated. 

Questions  concerning  the  immunes. — Without  attempting  to  go  into 
the  plans  in  detail,  the  1906  experiments  may  be  said  to  have  had  the 
following  objects  in  view:  To  determine  (1)  whether  natural  immunes 
or  those  which  have  acquired  immunit}^  are  best  suited  for  serum  pro- 
duction; (2)  what  percentage  of  either  natural  or  acquired  immunes 
may  be  expected  to  yield  a  potent  serum;  (3)  whether  the  "quick 
method"  or  the  "slow  method"  of  hype rimmunizat ion  pelds  the  best 
results;  (4)  whether  disease-producing  blood  from  different  outbreaks 
of  hog  cholera  is  equally  well  suited  for  the  purposes  of  hyperimmuni- 
zation;  (5)  whether  the  amounts  of  disease-producing  blood  used  for 
hyperimnmnization  might  be  reduced  without  affecting  the  potency  of 
the  serum,  and  (6)  how  long  after  the  last  injection  with  disease- 
producing  blood  the  imnumes  retain  tKe  power  to  furnish  a  potent 
senim. 

Questions  concerning  vaccination. — Many  (juestions  arise  in  con- 
nection with  the  practical  application  of  the  serum,  but  it  has  not 
thus  far  been  possible  to  attempt  to  answer  all  of  them.  The  prin- 
cipal points  we  had  in  mind  during  the  1906  experiments  were  as  fol- 
lows: To  determine  (1)  the  dose  of  serum  re(|uirod  to  protect  a  small 
hog  (25  to  50  pounds)  from  a  sinuiitaneous  injection  of  a  fatal  dose  of 
disease-producnig  blood;  (2)  the  duration  of  the  immunity  which 
follows  this  simultaneous  injection;  (3)  whether  it  is  necessary  to 

12840— No.  102—08 2 


18  PRODUCTION    OF   IMMUNITY   FROM    HOG   CHOLERA. 

produce  a  reaction  (i.  e.,  visible  illness  or  fever,  or  both)  in  order  to 
secure  a  lasting  immunity;  (4)  whether  the  administration  of  suffi- 
cient serum  to  prevent  a  reaction  will  t6nd  to  shorten  the  duration  of 
the  immunity  in  vaccinated  hogs;  (5)  whether  hogs  vaccinated  by  a 
simultaneous  injection  of  serum  and  disease-producing  blood  are 
likely  to  be  injured  or  stunted  in  growth;  (6)  whether  hogs  vaccinated 
by  this  "serum-simultaneous"  method  may  communicate  hog  cholera 
to  unvaccinated  hogs  by  association  with  them;  (7)  whether  a  lasting 
immunity  may  be  produced  by  the  injection  of  the  serum  alone ;  (8) 
whether  the  serum  alone  can  be  used  successfully  as  a  cure;  (9)  how 
long  the  serum  will  retain  its  potency,  and  (10)  whether  satisfactory 
results  may  be  obtained  by  vaccinating  suckling  pigs. 

GENERAL  PLAN  FOR  THE  PRODUCTION  OF  SERUM  IN  1006. 

The  immunes  used. — Eight  immune  hogs  were  to  be  hyperimmu- 
nized.  If  possible,  4  of  these  were  to  be  hogs  that  had  acquired  im- 
munity, while  the  remainder  were  to  be  natural  immunes.  Four  of 
these  8  hogs  (2  natural  immunes  and  2  that  possessed  acquired  im- 
munity) were  to  be  hyperimmunized  by  the  use  of  one  strain  of 
disease,  while  the  remaining  4  were  to  be  given  disease-producing 
blood  from  an  entirely  different  source.  * 

Method  of  hyperimmunization. — There  were  certain  general  features 
in  the  process  of  immunization  which  applied  alike  to  all  immunes 
treated  by  the  same  method.  First  of  all,  in  order  to  make  sure 
of  a  firm  immunity  and  to  avoid  losses  later,  a  preliminary  injection 
of  20  c.  c.  of  disease-producing  blood  was  given  each  immune.  After 
this  the  regular  process  of  hyperimmunization  was  begun.  Four 
of  the  immunes  were  hyperimmunized  by  the  quick  method  and 
4  by  the  slow  method  described  under  the  1905  "experiments. 

The  immunes  treated  by  the  quick  method  were  injected  with 
one  dose  of  disease-producing  blood,  the  amount  administered  being 
equal  to  1,000  c.  c.  of  disease-producing  blood  to  each  100  pounds 
of  body  weight.  Exactly  three  weeks  after  this  injection  blood  was 
drawn  from  the  tails  of  these  immunes  and  preserved  for  experi- 
mental use.  This  blood  drawing  from  the  immunes  was  repeated 
at  intervals  of  seven  or  eight  days  until  three  drawings  had  been 
made,  and  in  most  cases,  as  shown  by  the  detailed  records  which 
follow,  a  fourth  drawing  was  made  approximately  a  month  after 
the  third  drawing. 

The  immunes  treated  by  the  slow  method  were  injected  three 
times.  The  first  dose  was  in  the  proportion  of  100  c.  c.  of  disease- 
producing  blood  to  100  pounds  of  body  weight;  the  second  dose, 
which  followed  the  first  after  from  ten  to  fourteen  days,  was  in  the 
proportion  of  250  c.  c.  per  100  pounds  body  weight,  and  the  third 
and  last  dose,  which  was  given  approximately  twelve  days  after  the 


GENERAL    PLAN    FOR    PRODUCTION    OF    SERUM.  19 

second,  was  in  the  proportion  of  500  c.  c.  per  100  pounds  of  body 
weight.  Blood  drawings  from  the  immunes  hyperimmunized  by 
the  slow  method  were  begun  nine  or  ten  days  after  the  last  injection 
of  disease-producing  blood  and  repeated  at  intervals  of  seven  days. 

The  object  of  these  repeated  blood  drawings  from  the  immunes 
was  of  course  to  secure  blood  for  the  purpose  of  ascertaining  how 
long  after  the  last  injection  of  disease-producing  blood  the  immune 
retained  the  power  to  furnish  potent  serum.  These  different  draw- 
ings of  immune  blood — that  is,  some  of  them — were  tested  on  non- 
immune hogs,  as  shown  in  the  experiments  hereinafter  described. 

Method  of  collecting  and  preserving  the  immune  blood. — The  immune 
blood  was  drawn  in  all  cases  from  the  tails  of  the  immunes  and  was 
collected  in  a  wide,  sterilized  dish.  It  was  allowed  to  coagulate, 
and  the  clot  which  formed  was  then  subjected  to  pressure  in  order 
that  all  of  the  serum  might  be  separated  from  it.  Instead  of  a  clear 
serum,  therefore,  we  secured  always  a  serum  containing  large  num- 
bers of  red  blood  corpuscles  and  which  might  be  more  properly 
called  defibrinated  blood.  The  time  required  for  the  red  cells  to 
settle  and  the  very  considerable  loss  of  serum  which  would  have 
resulted  if  we  had  attempted  to  use  clear  serum  only,  owing  to  lack 
of  facihties  for  using  a  large  centrifuge,  made  it  necessary  to  employ 
the  serum  containing  red  cells.  In  applying  a  similar  method  to 
cattle  the  use  of  a  serum  containing  red  cells  would  no  doubt  be  con- 
sidered objectionable,  owing  to  the  danger  of  transmitting  some 
intercurrent  disease,  such  as  Texas  fever,  through  such  injections. 
Such  contingencies  were  not  likely  to  occur  in  the  case  of  hogs,  how- 
ever, and,  furthermore,  any  possible  danger  of  this  kind  was  no 
doubt  avoided  through  the  addition  of  an  antiseptic  to  the  serum 
immediately  after  it  was  drawn.  After  the  serum  had  been  com- 
pletely separated  from  the  clot  by  pressure  and  by  straining  through 
a  sterilized  cloth  it  was  mixed  with  a  5  per  cent  aqueous  solution  of 
carbolic  acid  in  the  proportion  of  9  parts  of  serum  to  1  of  carbolic- 
acid  solution,  thus  giving  a  0.5  per  cent  solution  of  carbolic  acid  in  the 
serum.  This  served  to  keep  the  serum  perfectly,  provided  it  was 
placed  at  once  in  sterilized  bottles  until  used.  It  should  bo  remem- 
bered that  all  of  the  hyperimmune  serum  used  in  the  experiments 
described  hereafter  consisted,  in  reality,  of  1  part  of  carbolic-acid 
solution  and  9  parts  of  .serum  and  red  cells. 

Sources  of  disease-jtroducing  hlood  irith  details  (fthe  hyperimmvnlza- 
tion. — As  already  stated,  disease-pro( hieing  blood  from  two  entirely 
distinct  sources  was  used  for  the  treatment  of  the  immunes.  One  of 
these  strains  of  (lisea.se  was  obtained  near  Scribner,  Nebr.,  and  is 
referred  to  as  the  "  Scribner  disease."  The  other  strain  of  di.sease  was 
secured  near  Alexandria.  Va.,  and  has  been  designated  the  "Syphax 
disease."     Blood  from  both  of  these  sources  proved  quite  virulent 


20  production"  OF    IMMUNITY    FROM    HOG    CHOLERA. 

when  administered  to  nonimmune  hogs;  the  blood  from  the  Scribner 
outbreak,  however,  appeared  to  produce  a  somewhat  more  acute 
type  of  disease  than  the  blood  from  the  Syphax  outbreak.  The 
immunes  hyperimmunized  with  blood  from  the  Scribner  outbreak  are 
designated  "Scribner  immunes,"  and,  depending  upon  the  method 
used  for  hyperimmunization,  the  individuals  have  been  called  "  Scrib- 
ner quick  immunes  "  or  "  Scribner  slow  immunes,"  as  the  case  might 
be.     The  same  plan  is  followed  in  speaking  of  the  "  Syphax  immunes." 

DESCRIPTION  OF  THE  SCRIBNEB  OUTBREAK. 

This  outbreak  of  hog  cholera  occurred  near  Scribner,  Nebr.,  in  the 
fall  of  1905.  When  this  locality  was  first  visited  by  one  of  us  it  was 
found  that  hog  cholera  of  a  virulent  type  existed  on  some  half  dozen 
farms.  Several  of  these  were  visited  and  the  sick  animals  were 
found  to  exhibit  the  usual  symptoms  of  hog  cholera,  and  at  autopsy 
the  usual  lesions,  such  as  intestinal  ulcers  and  ecchymoses  in  the 
various  organs,  were  noted.  From  one  of  these  infected  herds,  in 
which  the  final  loss  was  about  74  per  cent,  blood  was  secured  for 
experimental  purposes.  This  blood  was  collected  in  a  sterile  vessel, 
defibrinated,  and  kept  on  ice  until  it  was  used  at  the  Bureau  experi- 
ment farm  near  Ames,  Iowa,  for  the  injection  of  hogs  1395,  1393,  and 
1394,  which  received,  respectively,  1  c.  c,  2.5  c.  c,  and  5  c.  c,  subcu- 
taneously  on  November  18,  1905.  These  hogs  became  sick  six  days 
after  injection,  and  hogs  1393  and  1395  died  on  December  3,  1905. 
The  other  hog,  1394,  was  killed  on  December  1  to  secure  blood  for 
other  experiments.  Autopsies  which  were  held  on  2  of  these  hogs 
revealed  the  usual  lesions  of  hog  cholera. 

The  blood  of  hog  1394,  after  dilution,  was  filtered  through  a  Cham- 
berland  bougie,  and  the  filtered  blood  was  proven  to  possess  the  same 
degree  of  virulence  as  the  unfiltered  blood. 

A  portion  of  the  unfiltered  blood  of  hog  1394  was  placed  in  sealed 
glass  bulbs  and  preserved  on  ice  until  May,  1906,  when,  upon  injection, 
it  proved  to  be  quite  virulent,  and  hogs  inoculated  with  this  disease  or 
exposed  to  it  furnished  all  of  the  blood  used  in  hyperimmunizing  the 
so-called  "  Scribner  immunes." 

SCRIBNER  IMMUNES. 

Hyperimmunized  Immune  1286  (Quick  Method). 

This  hog  was  exposed  to  hog  cholera  on  August  17,  1905,  together 
with  another  of  about  the  same  weight  (50  pounds).  As  a  result  of 
this  exposure  hog  1286  exhibited  only  slight  indications  of  sickness 
and  soon  recovered,  although  the  other  hog  exposed  at  the  same  time 
died,  showing  at  autopsy  the  usual  lesions  of  hog  cholera.  In  order 
to  test  further  the  immunity  of  hog  1286  it  was  placed  in  the  station 


THE    SCRIBNER    OUTBREAK.  21 

exposure  pen  where  a  number  of  sick  hogs  were  kept.  This  hog 
failed  to  show  symptoms  of  disease  and  was  not  exposed  further  until 
the  summer  of  1906,  when  it  weighed  125  pounds. 

June  13,  1906,  hog  1286  received  subcutaneously  20  c.  c.  of  Scrib- 
ner  disease-producing  blood,  and  at  the  same  time  a  control  hog  was 
injected  with  10  c.  c  of  the  same  blood.  The  control  died,  while  hog 
1286  remained  well. 

June  25,  1906,  hog  1286  was  injected  subcutaneously  with  1,250 
c.  c.  of  Scribner  disease-producing  blood  secured  from  several  hogs. 
At  the  same  time  5  nonimmune  hogs  were  injected  to  serve  as  checks 
on  the  virulence  and  also  to  furnish  blood  for  treating  other  immunes. 
All  of  these  checks  became  very  sick  and  were  destroyed,  while  hog 
1286  remained  well  except  for  slight  soreness  following  the  injection. 

Blood  was  drawn  from  the  tail  of  hog  1286  as  follows: 

July  16,  1906,  356  c.  r.  defibrinated  blood  obtained. 
July  23,  1906,  300  c.  c.  defibrinated  blood  obtained. 
July  30,  1906,  250  c.  c-.  defibrinated  blood  obtained. 

This  blood  was  used  in  Experiments  I  and  II  described  in  another 
part  of  this  paper. 

Hyperimmunized  Immune  1313  (Quick  Method). 

This  hog  was  injected  subcutaneously  with  25  c.  c.  of  diluted  dis- 
eased blood  on  September  30,  1905.  Hog  1313  did  not  become 
noticeably  sick  as  a  result  of  the  injection,  although  the  blood  was 
of  a  fair  degree  of  virulence.  A  later  exposure  to  disease  in  the 
exposure  pen  was  likewise  without  effect  upon  this  hog.  No  further 
exposure  to  hog  cholera  was  made  until  the  summer  of  1906,  as 
described  below. 

June  13,  1906,  hog  1313  received  subcutaneously  20  c.  c.  of  Scrib- 
ner disease-producing  blood ;  a  nonimmune  hog  received  at  the  same 
time  10  c.  c.  of  the  same  blood.  The  check  dietl  of  hog  cholera,  but 
hog  1313  remained  well. 

July  5,  1906,  hog  1313,  which  weighed  130  pounds,  was  injected 
subcutaneously  with  1,300  c.  c.  of  Scribner  disease-producing  blood. 
Two  nonimmune  hogs  injected  at  the  same  time  with  2  c.  c.  each  of 
the  same  disease-producing  blood  became  very  sick  and  were  killed 
to  furnish  blood  for  the  other  experiments.  Hog  1313  was  a  little 
sore  on  the  day  following  the  injection;  this  soon  passed  away,  l)ut 
on  July  8  and  for  several  days  thereafter  the  hog  was  (piito  sluggish 
and  disinclined  to  eat.  By  July  13,  however,  rocovory  was  com- 
plete.    Blood  was  drawn  from  the  tail  of  hog  1313  lus  follows: 

July  26,  190<),  400  c.  c.  defibrinat("<l  blcKxl  ubtaincii. 
August  2,  190G,  465  r.  c.  defibrinated  \>\<h>(\  obtained. 
August  9,  1906,  450  c.  e.  defibrinated  bl(K)d  obtaine*!. 
September  6,  1906,  400  c.  c.  defibrinated  blotni  obtaiiu-d. 


22  PEODUCTION    OF    IMMUNITY   FROM    HOG    CHOLERA. 

The  blood  from  this  immune  was  used  in  Experiments  III  and 
IV,  which  are  described  in  the  following  pages : 

Hyperimmunized  Immune  1383  (Slow  Method). 

This  hog  was  injected  subcutaneously  on  November  17,  1905, 
with  5  c.  c.  of  blood  from  a  hog  sick  of  hog  cholera.  This  blood  as 
a  result  of  a  number  of  inoculations  was  found  to  cause  the  death  of 
somewhat  more  than  50  per  cent  of  the  inoculated  hogs.  Hog  1383 
showed  slight  sickness  after  injection,  but  soon  recovered  and  also 
remained  well  when  placed  in  the  exposure  pen  about  three  weeks 
later.  In  June,  1906,  this  hog  was  used  for  the  production  of  serum, 
as  described  below. 

June  13,  1906,  hog  1383  was  injected  subcutaneously  with  20  c.  c. 
of  Scribner  disease-producing  blood.  A  nonimmune  hog  was  in- 
jected at  the  same  time  with  10  c.  c.  of  the  same  blood.  The  non- 
immune died,  but  hog  1383  remained  well. 

June  25,  1906,  hog  1383  weighed  105  pounds  and  was  injected  sub- 
cutaneously with  105  c.  c.  of  Scribner  disease-producing  blood. 
Five  nonimmune  hogs  injected  at  the  same  time  with  10  c.  c.  each 
of  the  same  blood  became  very  sick  and  were  killed  to  furnish  blood 
for  other  experiments;  hog  1383  remained  well.  The  blood  used 
for  this  injection  was  the  same  as  that  used  for  the  hyperimmuni- 
zation  of  hog  1286,  and  the   same  checks  served  for  both  immunes. 

July  5,  1906,  hog  1383  received  a  second  mjection  consisting  of 
265  c.  c.  of  Scribner  disease-producing  blood.  The  blood  used  was 
the  same  as  that  used  for  the  injection  of  immune  1313  on  the  same 
date,  and,  as  stated  previously,  produced  hog  cholera  in  nonimmune 
animals  in  doses  of  2  c.  c.  Hog  1383  was  made  somewhat  sore  by  the 
injection,  but  was  well  again  after  two  or  three  days. 

July  14,  1906,  hog  1383  was  given  a  third  injection  of  Scribner  dis- 
ease-producing blood,  525  c.  c.  being  administered  subcutaneously. 
Tw^o  nonimmunes  injected  with  2  c.  c.  each  of  the  same  blood  as  con- 
trols on  the  virulence  of  the  blood  died  of  hog  cholera.  Hog  1383 
remained  well. 

This  injection  completed  the  hyperimmunization  of  hog  1383,  and 
blood  drawings  were  made  from  this  animal  as  follows : 

July  24, 1906,  392  c.  c.  defibrinated  blood  ojatained. 
July  31,  1906,  360  c.  c.  defibrinated  blood  obtained. 
August  7, 1906,  400  c.  c.  defibrinated  blood  obtained. 
August  14, 1906,  360  c.  c.  defibrinated  blood  obtained. 
September  4, 1906,  82  c.  c.  defibrinated  blood  obtained. 

The  blood  from  this  immune  proved  to  be  exceptionally  potent, 
and  it  was  therefore  used  in  a  number  of  different  experiments. 


HOGS    USED   TO    OBTAIN    HYPERIMMUNE    SERUM.  23 

Hyperimmuxized  Immune  1403  (Slow  Method). 

By  referring  to  Table  3  it  ^\'ill  be  seen  that  tliis  hog  was  one  of  those 
vaccinated  by  the  serum-simultaneous  method  in  the  1905  experi- 
ments. The  hog  showed  no  symptoms  of  disease,  either  as  a  result  of 
vaccination  or  of  the  subsequent  exposure  to  hog  cholera  in  the  expo- 
sure pen  on  December  27,  1905.  No  further  exposure  to  disease  was 
made  until  June,  1906,  when  hyperimmunization  was  begun.  The 
weight  of  the  hog  at  this  time  was  90  pounds. 

June  13,  1906,  hog  1403  was  injected  subcutaneoush'  with  20  c.  c. 
of  Scribner  disease-producing  blood.  A  control  injected  at  the  same 
time  with  10  c.  c.  of  the  same  blood  died,  whereas  hog  1403  remained 
well. 

June  25,  1906,  hog  1403  was  injected  subcutaneously  with  90  c.  c. 
of  the  same  disease-producing  blood  as  that  used  for  injecting  immunes 
1286  and  1383  on  the  same  date.  Hog  1403  was  not  visibly  affected 
by  the  injection. 

July  5,  1906,  hog  1403  was  injected  with  225  c.  c.of  Scribner 
disease-producing  blood.  The  same  blood  was  used  at  the  same  time 
for  injecting  immunes  1313  and  1383  and  four  control  hogs  as  previ- 
ously stated.  Immune  1403  was  sluggish  and  disinclined  to  eat  for 
several  days  following  the  injection,  but  by  July  9  had  apparently 
recovered. 

July  14,  1906,  hog  1403  was  injected  for  the  last  time  with  450  c.  c. 
of  Scribner  disease-producing  blood,  subcutaneously,  blood  from  the 
same  source  being  used  at  the  same  time  for  the  injection  of  immune 
1383  and  two  controls,  as  stated  above.  Hog  1403  showed  about  the 
same  disturbance  as  was  noted  after  the  second  injection,  but  was 
well  again  in  four  or  five  days. 

Blood  drawings  were  made  from  immune  1403  as  follows: 

July  24,  190C,  395  c.  c.  defibrinaUHl  hUxjd  obtained. 
July  31, 19(K},  390  c.  c.  d«ifibrinaled  bl(K)d  obtained. 
.\ugust  7,  190(i,  400  c.  e.  defibrinated  l)l(K)d  obtained. 
August  14,  1900,  3G0  c.  c.  defibrinated  l)lood  obtained. 
September  14,  HKMi,  3(50  c.  r.  defibrinated  l)l(M)d  obtained. 

DESCRIPTION  OF  THE  SYPHAX  OUTBREAK. 

This  outbreak  of  hog  cholera  occurred  near  Alexandria,  Va.  At 
the  time  the  first  syinj)toins  of  ilhiess  were  ojj.served,  on  S('j)teini)er  6, 
1905,  there  were  37  hogs  in  the  herd.  The  disea.se  did  not  ])rogress 
verj'  rapidly,  but  nevertheles.s  all  of  the  hogs  were  finally  attacke<i  by 
the  disease.  At  the  time  the  herd  was  first  visited  by  representa- 
tives of  this  Btireaii  only  9  hogs  remained  alive,  and  some  of  these 
were  killed,  while  others  died,  the  final  result  being  that  3  hogs  out  of 
the  37  that  were  attacked  recovered.     The  lesions  found  at  autopsy 


24  PRODUCTION   OF    IMMUNITY   FROM    HOG   CHOLERA. 

were  such  as  are  usually  met  with  in  hog  cholera,  except  that  the  pul- 
monary lesions  in  some  of  the  animals  were  rather  more  prominent 
than  we  have  ordinarily  found  to  be  the  case. 

Blood  from  one  of  the  sick  animals  in  this  herd  served  as  the 
starting  point  for  the  strain  of  disease  from  which  blood  was  secured 
to  hj'perimmunize  the  "Syphax  immunes."  Filtered  blood  from  this 
Syphax  herd  produced  hog  cholera  when  injected  into  nonimmune 
hogs,  even  though  it  was  found  to  be  free  from  all  of  the  ordinary 
bacteria. 

SYPHAX  IMMUNES. 
Hyperimmunizei)  Immune  1392  (Quick  Method).  ' 

This  hog,  with  5  others,  was  injected  subcutaneously  on  November 
17,  1905,  with  5  c.  c.  of  ho^-cholera  blood.  All  became  sick  as  a 
result  of  this  inoculation  and  4  died,  hog  1392  and  one  other  finally 
recovering.  Hog  1392  was  placed  in  the  exposure  pen  in  December, 
1905,  and  remained  well.  This  hog  exhibited  quite  typical  symptoms 
of  hog  cholera  after  the  first  blood  injection,  and  the  immunity  sub- 
sequently exhibited  must  be  regarded  as  having  been  acquired  through 
this  attack  of  disease. 

June  13,  1906,  hog  1392  received  20  c.  c.  of  virulent  Scribner  dis- 
ease-producing blood  in  common  with  all  of  the  immunes  which  were 
later  hyperimmunized  with  blood  from  either  the  Scribner  or  Syphax 
outbreaks.     Hog  1392  remained  well. 

July  13,  1906,  hog  1392,  which  at  that  time  weighed  130  pounds, 
received  subcutaneously  1,300  c.  c.  of  Sj^^hax  disease-producing  blood. 
Five  control  hogs  which  were  injected  at  the  same  time  with  5  c.  c.  of 
the  same  blood  became  very  sick  ancl  were  killed  to  furnish  blood  for 
other  experiments.  Hog  1392  was  somewhat  stiff  and  sore  on  the 
two  days  following  the  injection,  but  otherwise  remained  well. 
Drawings  of  blood  from  immune  1392  were  made  as  follows: 

August  3,  1906,  375  c.  c.  defibrinated  blood  obtained. 
August  10.  1906,  435  c.  c.  defibrinated  blood  obtained. 
August  17,  1906.  500  c.  c.  defibrinated  blood  obtained. 
September  17,  1906.  100  c.  c.  defibrinated  blood  obtained. 

Hyperimmunized  Immune  1274  (Quick  Method). 

This  hog  was  first  exposed  to  hog  cKblera  on  July  22,  1905,  by  the 
subcutaneous  injection  of  0.25  c.  c.  of  hog-cholera  blood.  Another 
hog  injected  at  the  same  time  died,  but  hog  1274  did  not  become  sick, 
nor  did  this  hog  show  symptoms  of  disease  when  placed  in  the  expo- 
sure pen  some  weeks  later.  The  records  indicate  that  this  hog  pos- 
sessed quite  a  high  degree  of  natural  immunity. 

June  13,  1906,  hog  1274  was  injected  subcutaneously  with  20  c.  c. 
of  Scribner  disease-producing  blood  along  with  the  other  immunes. 
No  ill  effects  were  noticed  as  a  result  of  this  inoculation. 


THE    SYPHAX    OUTBREAK.  25 

July  26,  1906,  this  hog,  which  weighed  at  that  time  125  pounds, 
was  injected  subcutaneously  with  1,250  c.  c.  of  Syphax  disease- 
producing  blood,  and  4  control  hogs  were  injected  at  the  same  time 
with  from  2  c.  c.  to  5  c.  c.  each  of  the  same  blood.  All  of  the  controls 
became  very  sick  and  were  killed  to  furnish  blood  for  other  experi- 
ments. Hog  1274  showed  no  marked  effects  from  the  injection. 
Drawings  of  blood  from  this  hog  were  made  as  follows. 

August  16, 1906,  450  c.  c.  defibrinated  blood  obtained. 
August  23,  1906,  450  c.  c.  defibrinated  blood  obtained. 
September  1,  1906, 378  c.  c.  defibrinated  blood  obtained. 
October  1,  1906,  700  c.  c.  defibrinated  blood  obtained. 

Hyperimmunized  Immune  1310  (Slow  Method). 

This  hog,  with  one  other,  was  injected  \Wth  hog-cholera  blood  on 
September  29,  1905;  the  mate  to  hog  1310  showed  slight  indisposition 
after  the  injection,  but  hog  1310  remained  well.  Both  hogs  were 
later  placed  in  the  exposure  pen.  Hog  1310  did  not  thrive  there,  but 
never  became  plainly  sick.  After  removal  from  the  exposure  pen 
this  hog  regained  its  vigor,  and  on  July  13,  1906,  at  which  time  the 
hyperimmunization  was  begun,  its  weight  was  180  pounds. 

June  13,  1906,  the  preliminary  injection  of  20  c.  c.  of  virulent 
Scribner  disease-producing  blood  was  made.  No  visible  reaction 
followed  this  injection. 

July  13,  1906,  hog  1310  was  injected  subcutaneously  with  180  c.  c. 
of  Syphax  disease-producing  blood  from  the  same  source  as  that  used 
for  the  injection  of  immune  hog  1392  on  the  same  date.  Hog  1310 
remained  well,  although  the  control  hogs  injected  at  the  same  time 
contracted  hog  cholera. 

July  26,  1906,  hog  1310  was  injected  subcutaneously  ^vith  400  c.  c. 
of  Syphax  disease-producing  blood  from  the  same  source,  as  that 
used  for  the  injection  of  immune  hog  1274  on  the  same  date.  Hog 
1310  showed  practically  no  disturbance  of  liealth  after  this  injection, 
although  the  control  animals  injtx'ted  with  a  much  smaller  amount 
of  the  dijsease-producing  blood  contracted  hog  cholera. 

August  7,  1906,  hog  1310  was  injected  subcutaneously  with  900  c.  c. 
of  vS}^)hax  disease-producing  blood.  Two  noninuuune  hogs  injected 
subcutaneously  with  2  c.  c.  and  5  c.  c.  of  the  same  blood  contracted 
hog  cholera  and  died.  With  the  excej)tion  of  a  Httle  sorene.s.s.  hog 
1310  remained  well. 

Blood  was  drawn  from  this  imnuinc  as  follows: 

.\ugU8t  16,  190f),  450  c.  0.  defibrinated  blood  obtained. 
.\ugust  23,  1906,  450  c.  c.  defibrinated  IdcHxl  dbtaiued. 
September  1.  1906,  540  r.  c.  defibrinated  Itlond  dbtuined. 
October  1,  1906,  450  c.  e.  defibrinatctl  blood  obtained. 


26  .     PRODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 

Hyperimmi'nized  Immune  1297  (Slow  Method). 

This  hog  weighed  approximately  55  pounds  on  September  13,  1905, 
at  which  time  it  was  injected  subcutaneously  with  hog-cholera  blood. 
No  sickness  followed  this  injection  and  a  later  exposure  in  the  ex- 
posure pen  was  likewise  without  result  as  far  as  could  be  observed, 
though  a  mild  attack  at  this  time  may  have  passed  unobserved. 

June  13,  1906,  this  hog  received,  with  the  other  immunes,  a  prelim- 
inary injection  of  20  c.  c.  of  Scribner  disease-producing  blood  without 
any  symptoms  of  disease  being  caused. 

June  29,  1906,  hog  1297  was  injected  subcutaneously  with  175  c.  c. 
of  Syphax  disease-producing  blood.  Two  nonimmune  hogs  in- 
jected at  the  same  time  with  2  c.  c.  each  of  the  same  blood  died  of 
hog  cholera.     Hog  1297  remained  well. 

July  13, 1906,  hog  1297  was  injected  subcutaneously  with  440  c.  c.  of 
Syphax  disease-producing  blood  from  the  same  source  as  that  used 
for  the  injection  of  immunes  1310  and  1392  on  the  same  date.  All  of 
the  checks  injected  wath  the  same  lot  of  blood  became  sick  and  either 
died  or  were  killed  to  furnish  blood  for  other  experiments.  Hog  1297 
remained  well  except  for  slight  soreness  following  the  injection. 

July  26,  1906,  hog  1297  was  again  injected  with  Syphax  disease- 
producing  blood,  the  dose  being  850  c.  c.  of  blood  fi'oin  the  same 
source  as  that  used  for  the  injection  of  immunes  1274  and  1310  on 
the  same  date.  As  previously  stated,  controls  injected  at  the  same 
time  became  sick  and  were  killed  to  furnish  blood  for  other  experi- 
ments.    Blood  was  drawn  from  immune  1294  as  follows: 

August  4,  1906,  390  c.  c.  defibrinated  blood  obtained. 
August  11,  1906,  300  c.  c.  defibrinated  blood  obtained. 
August  18,  1906,  500  c.  c.  defibrinated  blood  obtained. 
September  17,  1906,  360  c.  c.  defibrinated  blood  obtained. 

It  has  been  previously  stated  that  it  was  intended  to  use,  for  the 
production  of  hyperimmune  serum,  4  naturally  imnmne  hogs  and  4 
which  had  acquired  immunity  through  an  attack  of  hog  cholera. 
When  it  came  to  the  actual  working  out  of  this  plan,  however,  as  is 
shown  in  the  preceding  pages,  we  were  only  able  to  secure  1  hog 
(1392)  that  had  recovered  from  an  undoubted  attack  of  hog  cholera; 
2  others  (1286  and  1383)  had  shown  slight  though  not  characteristic 
symptoms  of  that  disease,  while  the  fourth  (1403),  among  those  that 
were  considered  as  having  acquired  immunity,  had  been  vaccinated 
in  1905,  but  had  not  shown  symptoms  of  illness  at  any  time  after 
being  vaccinated.  In  regard  to  this  last-mentioned  hog,  it  should 
be  noted  that  it  has  been  found  to  be  frequently  the  case  that  sus- 
ceptible hogs  may  show  no  symptoms  following  vaccination  and  yet 
may  secure  through  this  treatment  a  firm  and  lasting  immunity,  and 
we  believe  this  to  have  been  the  case  with  hog  1403.  The  remaining 
4  immunes,  1274,  1297,  1310,  and  1313,  were  not  vaccinated,  bu>/ 


VACCINATION    EXPERIMENTS.  27 

nevertheless  they  showed  no  symptoms  of  disease  when  exposed  to 
hog  cholera,  and  we  may  therefore  with  a  reasonable  degree  of  assur- 
ance look  upon  these  hogs  as  being  naturally  immune.  From  what 
has  just  been  said  it  becomes  evident  that  the  plan  to  test  the  rela- 
tive capability  of  ''natural"  and  ''acquired"  immunes  to  produce  a 
potent  protective  serum  could  not  be  carried  out  on  as  extensive  a 
scale  as  was  desired,  but  nevertheless  it  was  hoped  that  considerable 
information  might  be  acquired  from  a  comparison  of  serum  from  hog 
1392  with  serum  from  the  hogs  that  appeared  to  possess  a  natural 
immunity. 

VACCINATION   EXPERIMENTS   IN   1906. 

The  experiments  as  originally  planned  were  necessarily  modified 
more  or  less  owing  to  the  existence  of  conditions  which  could  not  be 
foreseen,  but  notwithstanding  the  fact  that  the  original  plan  was 
not  carried  out  in  all  instances  it  may  perhaps  lead  to  a  better  under- 
standing of  the"  experiments  which  are  now  to  be  described  if  this 
plan  is  briefly  outlined. 

The  experiments  with  serum  from  each  of  the  hyperimmunized 
immunes  were  to  consist  of  two  sections,  (1)  preliminarv'  experiments 
and  (2)  secondary-  experiments. 

Preliminary  experiments. — These  experiments  were  designed  in  the 
main  to  determine  the  potency  of  the  immime  serum.  A  number 
of  nonimmune  hogs  were  to  be  injected  with  2  c.  c.  each  of  disease- 
producing  blood.  A  few  of  these  were  to  be  left  untreatetl  as  con- 
trols, while  the  others  were  to  receive  sinmltaneously  with  the  disease- 
producing  blood  varying  doses  of  the  immune  serum.  Uninoculated 
hogs  were  to  be  placed  in  the  pens  with  the  treated  as  well  as  the 
untreated  hogs  to  determine  the  likelihootl  of  disease  being  trans- 
mitted by  the  treated  hogs.  Any  survivors  from  the  preliininar}- 
experiments  were  to  be  reserved  for  exiK)sure  to  hog  cholera  at  a 
later  date. 

Secondary  experiments. — These  were  intended  to  determine  many 
questions  of  practical  interest,  the  preliminary  experiments  having 
already  established  the  degree  of  potency  of  the  different  sera  when 
injected  simultaneously  with  diseased  blood.  In  these  secondary 
experiments  four  lots  of  hogs  were  to  be  treated. 

Ijot  1.  These  hogs  were  to  receive  disease-producing  blood  with 
the  minimum  dose  of  serum  required  to  protect. 

I»t  2.  Tliese  were  to  receive  disease-producing  blood  with  double 
the  minimum  amount  of  serum  required  to  ])r()tect. 

Ijot  3.  These  were  to  receive  the  minimum  amount  of  serum  alone. 

Ijoi  4.  This  lot  was  to  receive  the  maximum  amount  of  serum  alone. 

Controls  were  of  course  to  be  injected  with  di.sease-producing  blood 
alone,  and,  as  in  the  preliminary  experiments,  hogs  were  to  be  placed 


28  PRODUCTION   OP   IMMUNITY   FROM    HOG   CHOLERA. 

in  the  pens  with  the  treated  as  well  as  the  untreated  ones  to  deter- 
mine the  likelihood  of  disease  being  conveyed  to  others  by  contact. 
The  survivors  from  these  experiments  were  to  be  divided  into  two 
lots,  one  to  be  exposed  within  thirty  days  after  vaccination,  the  other 
to  be  placed  in  a  quarantine  pasture  and  not  subjected  to  exposure 
until  the  expiration  of  three  or  more  months.  As  will  be  explained 
later,  the  exposure  to  hog  cholera  could  not  be  carried  out  in  the 
manner  planned,  owing  to  an  outbreak  of  disease  among  the  hogs  in 
the  quarantine  pasture. 

In  addition  to  carrying  out  these  preliminary  and  secondary  experi- 
ments, serum  from  certain  of  the  immunes  was  to  be  used  in  special 
experiments  with  suckling  pigs,  and  also  for  the  purpose  of  testing 
the  curative  value  and  the  keeping  quality  of  the  serum,  and  other 
questions  of  more  or  less  practical  importance.  Except  in  the  case 
of  these  special  experiments  the  tests  with  the  serum  from  the  Syphax 
and  Scribner  immunes  are  described  separately. 

TESTS   OF    SERUM    FROM    HOGS   HYPERIMMUNIZED    WITH    BLOOD    FROM 
THE    SCRIBNER  OUTBREAK. 

The  description  of  the  outbreak  from  which  this  strain  of  disease 
was  derived  has  aheady  been  given  on  page  20,  and  the  history  of 
the  immunes  with  the  details  of  hyperimmunization  and  time  of  the 
various  blood  drawings  has  also  been  given. 

Serum  from  Immune  1286  (Quick  Method). 

Experiment  I. — Preliminary  experiment  with  first  drawing  of  serum. 

This  experiment  was  carried  out  in  accordance  with  the  plan  origi- 
nally decided  upon  for  all  preliminary  experiments.  Eight  hogs  were 
injected;  2  of  these  received  disease-producing  blood  simultaneously 
with  5  c.  c.  of  serum,  2  received  disease-producing  blood  with  10  c.  c. 
of  serum,  2  disease-producing  blood  with  15  c.  c.  of  serum,  and  2 
disease-producing  blood  alone.  These  four  lots  of  hogs  were  placed 
in  separate  pens  with  an  uninoculated  check  in  each  pen.  The  hogs 
which  received  only  5  c.  c.  and  10  c.  c.  of  immune  serum  with  the 
diseased  blood  became  distinctly  sick,  but  recovered;  the  uninocu- 
lated checks  in  the  pens  with  these  did  not  contract  disease,  however, 
in  either  case;  the  2  hogs  which  received  15  c.  c.  of  immune  serum 
with  the  disease-producing  blood  did  not  become  sick,  and  their  pen 
check  also  remained  well.  The  2  hogs  which  received  disease- 
producing  blood  alone  sickened  and  died  promptly  after  injection, 
and  at  autopsy  exhibited  the  usual  lesions  of  hog  cholera;  the  unin- 
oculated pen  check  with  these  last  2  hogs  contracted  disease  from 
them  and  showed  lesions  of  hog  cholera  when  destroyed  on  August 
4,  1906. 


EXPEKIMENT8    WITH    SERUM    FROM    SCRIBNER   IMMUNES. 


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30  PRODUCTION    OF    IMMUNITY    FROM    HOG    CHOLERA. 

The  protective  power  of  1286  serum  is  well  shown  by  this  experi- 
ment, in  which  all  the  vaccinated  hogs  survived,  while  those  which 
received  disease-producing  blood  alone  died  promptly.  It  is  evi- 
dent also  that  5  c.  c.  of  this  serum  is  probably  the  least  amount  that 
would  protect,  as  even  those  which  received  10  c.  c.  showed  some 
signs  of  illness.  In  accordance  with  the  original  plan,  the  survivors 
from  this  experiment  were  placed  in  a  large  quarantine  pasture  to  be 
reserved  for  exposure  at  a  later  date. 

Many  other  hogs  which  had  been  treated  in  various  ways  with 
different  sera,  together  with  a  considerable  number  of  uninoculated 
control  animals,  were  placed  in  this  pasture  from  time  to  time  for  the 
same  purpose.  In  some  way  hog  cholera  was  accidentally  introduced 
into  this  pasture  toward  the  end  of  October,  1906,  as  shown  by  the 
sickness  and  death  of  some  of  the  hogs,  the  autopsies  revealing  typical 
lesions  of  hog  cholera.  The  first  hogs  to  show  symptoms  of  hog 
cholera  in  this  pasture  were  the  unvaccinated  controls  about  October 
15,  and  the  first  death  among  these  occurred  October  25.  This  acci- 
dental exposure,  to  which  a  large  number  of  our  vaccinated  hogs  and 
unvaccinated  control  hogs  were  subjected,  resulted  in  the  death  of 
80  per  cent  of  all  the  unvaccinated  hogs. 

Table  4  shows  that  pen  checks  1522  and  1525,  which  were  placed 
in  the  quarantine  pasture  with  the  vaccinated  hogs,  both  died  of  hog 
cholera  as  a  result  of  this  exposure,  while  none  of  the  vaccinated  hogs 
were  made  sick.  Although  this  exposure  was  accidental,  it  occurred 
approximately  three  months  after  vaccination,  and  therefore  in  this 
instance  did  not  interfere  with  our  plans.  As  the  treated  hogs  did 
not  become  sick  from  the  pasture  exposure,  they  were  placed  in  the 
exposure  pen  where  hogs  sick  of  hog  cholera  (Scribner  disease)  were 
kept.  Conditions  in  this  pen  were  extremely  unfavorable  for  the 
general  health  of  the  hogs  exposed,  and  the  disease  was  very  virulent, 
as  shown  by  the  death  of  all  the  check  animals.  It  will  be  seen  from 
Table  4  that  treated  hogs  1520,  1521,  1523,  and  1524  all  became 
unthrifty.  One  of  these  was  killed  and  3  died  about  thirty  days  after 
being  placed  in  the  exposure  pen,  while  1526  and  1527,  the  2  remain- 
ing vaccinated  hogs,  remained  well.  None  of  the  first  4  hogs  men- 
tioned showed  any  of  the  lesions  of  hog  cholera  at  autopsy,  and  there 
seems  little  room  to  doubt  that  these  hogs  died  of  unthriftiness  and 
impaired  vitality  caused  by  the  original  vaccinating  dose.  It  will  be 
remembered  that  they  became  sick  after  vaccination,  and  they  should 
therefore  have  been  subsequently  much  more  resistant  to  hog  cholera 
than  the  2  hogs  (1526  and  1527)  which  showed  no  such  symptoms. 
We  consider  it  quite  evident,  therefore,  that  the  attack  of  hog  cholera 
brought  on  by  vaccination  weakened  the  constitution  of  those  which 
received  serum  in  doses  of  5  c.  c.  and  10  c.  c.  to  such  an  extent  that 
they  could  not  withstand  the  unfavorable  conditions  existing  in  the 


EXPERIMENTS    WITH    SERUM    FROM    SCRIBNER   IMMUNES.         31 

exposure  pen.,  The  deaths  of  the  checks  in  the  quarantine  pasture 
shows  that  the  pasture  exposure  was  sufficient  to  cause  the  death  of 
nonimmune  hogs.  The  fact  that  all  the  vaccinated  hogs  survived 
shows  that  when  given  the  same  exposure  at  the  end  of  three  months 
the  immunity  remained  quite  firm. 

Experiment  II. — Secondary  experiment  with  first  drawing  of  serum. 

• 

In  the  secondary  experiment  with  serum  from  immune  1286  the 
doses  of  serum  used  with  disease-producing  blood  were  10  c.  c,  which 
was  considered  the  minimum  safe  dose,  and  20  c.  c,  double  the 
amount  needed  to  surely  protect,  as  planned.  A  number  of  hogs  in 
this  experiment  were  also  mjected  with  serum  alone.  The  results 
which  followed  vaccination  are  in  complete  agreement  with  those 
obtained  in  Experiment  I.  The  3  hogs  injected  with  disease-produc- 
ing blood  alone  contracted  hog  cholera  and  died,  and  the  uninoculated 
hog  in  this  same  pen  also  died  of  hog  cholera  contracted  from  those 
which  received  the  disease-producing  blood  alone.  Of  6  hogs  injected 
vnih  diseased  blood  plus  10  c.  c.  of  serum,  all  became  sick  and  1  died; 
the  remaining  5  finally  recovered.  None  of  the  6  hogs  injected  with 
disease-producing  blood  plus  20  c.  c.  of  immune  serum  showed  any 
illness  after  vaccination,  and  those  injected  with  serum  alone  likewise 
remained  well.  One  of  the  2  pen  checks  exposed  to  the  lot  of  vacci- 
nated hogs  which  sickened  after  vaccination  contracted  hog  cholera 
and  was  killed;  the  other  remained  well. 

Nineteen  days  aft^r  vaccination,  as  shown  by  Table  5,  half  of  the 
vaccinated  hogs  which  had  received  20  c.  c.  of  serum  with  disease- 
producing  blood  were  placed  in  the  Scribner  exposure  pen.  About 
the  same  time  2  hogs  which  had  received  20  c.  c.  of  serum  alone,  2 
which  received  10  c.  c.  of  serum  alone,  and  1  uninoculated  pen  check 
were  placed  in  the  same  exposure  pen.  Of  the  hogs  which  were  made 
sick  by  vaccination  with  10  c.  c.  of  serum  plus  diseased  blood,  3  were 
plttced  in  the  exposure  pen  thirty-four  days  after  vaccination,  together 
with  1  pen  check. 

Both  of  the  pen  checks  (1569  and  1576)  which  were  placed  in  the 
exposure  pen  with  the  treated  hogs  died  of  hog  cholera,  although  not 
one  of  the  10  vaccinated  hogs  showed  any  visible  signs  of  illness. 

As  the  Scribner  strain  of  disease  had  been  used  exclusively  for  the 
hyperimmunization  of  hog  1286,  which  furnished  the  serum,  and  as 
the  diseased  blood  u.sed  in  the  simultaneous  vaccination  was  of  the 
Scribner  strain,  and  furthermore  as  the  exposure  pen  in  which  the.se 
hogs  were  placed  to  test  their  immunity  contained  only  the  Scribner 
strain  of  di.sease,  it  was  deemed  desirable  to  aj^certain  the  effect  of  a 
different  strain  of  disease  on  the  vaccinated  hogs.  An  exposure  pen 
containing  only  the  Syphax  strain  of  disea.se  was  therefore  prepared, 
and  hogs  1570,  1571,  1573,  1578,  1579,  1582,  and  1584  were  placed  in 


32 


PRODUCTION    OF    IMMUNITY   FROM    HOG    CHOLERA. 


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it  about  September  15,  1906.  On  October  30,  1906, 
the  3  remaining  hogs  which  had  %vithstood  exposure 
in  the  Scribner  exposure  pen  were  also  placed  in  the 
Syphax  exposure  pen.  None  of  the  vaccinated  hogs 
became  sick  as  a  result  of  this  second  exposure, 
although  an  unprotected  hog  exposed  at  the  same 
time  contracted  hog  cholera  and  died.  This  would 
indicate  that  the  serum  alone  served  to  confer  im- 
munity which  might  last  for  six  weeks,  although  the 
possibilit}"  of  the  immunity  being  heightened  by  the 
exposure  in  the  Scribner  exposure  pen  can  not  be 
overlooked. 

The  remainder  of  the  vaccinated  hogs  in  Experi- 
ment II,  together  with  pen  check  1577,  none  of  which 
were  exposed  in  the  exposure  pen,  were  placed  in  the 
quarantine  pasture  to  await  a  later  exposure.  As  pre- 
viously explained,  however,  our  plans  in  this  respect 
were  interfered  Avith  by  an  unforeseen  outbreak  of 
hog  cholera  among  the  control  hogs  which  were  being 
kept  wdth  the  vaccinated  hogs  in  this  quarantine  pas- 
ture. This  outbreak  occurred  approximately  two 
and  one-half  months  after  vaccination  of  the  hogs  in 
Experiment  II.  The  vaccinated  hogs  in  this  experi- 
ment which  were  exposed  in  this  manner  consisted  of 
2  that  had  received  10  c.  c.  of  serum  \nth  2  c.  c.  of 
diseased  blood,  3  that  had  received  20  c.  c.  of  serum 
with  diseased  blood,  and  2  each  of  those  which  re- 
ceived 20  c.  c.  and  10  c.  c.  of  immune  serum  alone. 
(See  Table  5.)  One  of  those  that  had  received  10  c. 
c.  of  serum  alone  was  killed  by  other  hogs  the  day 
it  was  placed  in  the  pasture.  Check  hog  1577  died 
of  hog  cholera  as  a  result  of  this  exposure.  Of  the 
vaccinated  hogs,  both  of  those  injected  with  20  c.  c. 
of  semm  alone  died  of  hog  cholera;  the  remaining 
one  injected  with  10  c.  c.  of  seriun  alone  died,  but  no 
marked  lesions  were  found  at  autopsy.  The  hogs 
which  were  given  10  c.  c.  and  20  c.  c.  of  serum 
simultaneously  with  di.seased  blood  remained  well. 
The  3  hogs  vaccinated  witli  20  c.  c.  of  serum  jihis 
(li.sea.sed  blood  which  remained  well  in  the  (juaran- 
tine  ])asture  were  later  j)laced  in  the  Scribner  ex- 
posure pen,  where  they  again  remained  well. 

In  .summarizing  the  experiments  ^^'ith  the  first 
drawing  of  .scrum  from  immune  12<S(),  we  find  that 
IS  hogs  were  treated  by  the  serum-simultaneous 
12840— No.  102— 1'« 3 


I- 


34  PRODUCTION    OF   IMMUNITY   FROM    HOG   CHOLERA. 

method,  the  dose  of  serum  varying  from  5  c.  c.  to  20  c.  c,  and  that  only 
one  of  these  died  from  the  vaccination,  although  all  that  received 
less  than  15  c.  c.  of  serum  became  sick.  Of  the  5  hogs  which  were 
injected  \\'ith  diseased  blood  alone,  all  died  of  hog  cholera.  Eight 
hogs  were  injected  with  serum  alone,  no  ill  effects  whatever  following 
the  injection. 

In  regard  to  the  exposure  to  hog  cholera  after  vaccination,  we  find 
that  all  vaccinated  hogs,  whether  treated  with  serum  alone  or  with 
a  combination  of  serum  and  disease-producing  blood,  were  rendered 
completely  immune  from  hog  cholera  for  at  least  three  weeks.  It 
appears,  however,  from  the  death  of  hogs  1580  and  1581  that  the 
scrum  of  immune  1286  when  given  alone,  even  in  doses  of  20  c.  c, 
does  not  afford  protection  to  hogs  weighing  from  25  to  40  pounds  for 
as  long  as  two  and  one-half  months. 

In  so  far  as  the  first  drawing  of  serum  from  immune  1286  is  con- 
cerned, we  may  conclude  that  (1)  when  given  in  sufficient  dose  it 
protects  hogs  completely  from  a  fatal  dose  of  disease-producing  blood 
administered  simultaneously  with  the  serum;  (2)  that  the  hogs 
which  survive  vaccination  by  the  serum-simultaneous  method  are 
rendered  immune  for  a  period  of  at  least  two  and  one-half  months; 
(3)  that  hogs  which  show  no  visible  reaction  after  this  treatment 
are  rendered  quite  as  resistant  as  those  which  were  made  distinctly 
sick  by  the  protective  inoculation;  (4)  if  a  sufficient  dose  of  serum  is 
not  given  ^^^ith  the  disease-producing  blood  the  vitality  of  the  vacci- 
nated hog  is  apt  to  be  impaired;  (5)  hogs  vaccinated  with  serum 
alone  are  rendered  immune  for  a  period  of  three  weeks,  but  this  immu- 
nity does  not  last  two  and  one-half  months;  (6)  uninoculated  hogs 
placed  in  pens  with  others  vaccinated  by  the  serum-simultaneous 
method  did  not  contract  hog  cholera  from  them  unless  the  vaccinated 
hogs  themselves  became  distinctly  sick. 

Serum  from  Immune  1313  (Quick  Method). 
Experiment  III. — Preliminary  experiment  with  first  drawing  of  serum. 

This  experiment  was  carried  out  in  the  same  manner  as  Experi- 
ment I,  the  doses  of  immune  serum  being  5  c.  c,  10  c.  c.  and  15  c.  c; 
at  the  same  time  each  hog  was  injected  subcutaneously  with  2  c.  c.  of 
disease-producing  blood.  Controls  were  injected  at  the  same  time 
with  an  equal  amount  of  the  same  disease-producing  blood  alone. 
Of  the  6  hogs  treated  with  both  serum  and  disease-producing  blood, 
none  showed  any  symptoms  of  sickness  after  vaccination,  although 
both  of  the  hogs  which  were  injected  with  an  equal  amount  of  the 
same  disease-producing  blood  alone  became  very  sick  and  one  of 
them  died.     The  pen  checks  which  were  placed  with  each  lot  of 


EXPERIMENTS  WITH  SERUM   FROM   SCRIBNER   IMMUNES.  35 

vaccinated  hogs  did  not  contract  disease  from  them,  but  the  pen 
check  with  the  controls  1751  and  1752  contracted  disease  from  them 
and  died. 

Approximately  three  weeks  after  vaccination  all  of  the  treated 
hogs  with  their  pen  checks  were  placed  in  the  quarantine  pasture. 
(See  Table  6.)  The  accidental  outbreak  of  ho^  cholera  in  this  pasture 
began  about  this  time,  so  that  these  hogs  may  be  considered  as  having 
been  exposed  to  disease  about  the  time  that  they  were  placed  in  the 
pasture.  None  of  the  vaccinated  hogs  became  sick  as  a  result  of  this 
exposure ;  2  of  the  pen  checks  became  sick  and  1  died ;  the  remaining 
check  did  not  show  symptoms  of  sickness.  At  a  later  date,  in  order 
to  further  test  their  immunity,  the  vaccinated  hogs,  with  the  check 
which  did  not  become  sick  in  the  pasture,  were  placed  in  the  Scrib- 
ner  exposure  pen,  but  none  of  them  became  sick. 

Experiment  IV. — Secondary  experiment  with  first  drawing  of  serum. 

The  second  experiment  with  this  serum  was  carried  out  in  the 
manner  planned  for  secondarj^  experiments  except  that  the  min- 
imum dose  of  serum  used  was  10  c.  c,  even  though  5  c.  c.  had  given 
protection  in  the  preliminary  experiment.  That  this  dose  was  not  too 
great  is  shown  by  the  sickness  and  death  of  one  of  the  serum-simul- 
taneous vaccinated  hogs  that  received  10  c.  c.  of  serum.  As  may  be 
seen  from  Table  7,  6  hogs  were  injected  with  10  c.  c.  of  serum  plus 
2  c.  c.  of  disease-producing  blood,  while  6  received  20  c.  c.  of  serum 
with  the  disease-producing  blood.  Four  hogs  were  injected  with  10 
c.  c.  of  serum  alone  and  a  like  number  received  20  c.  c.  of  serum 
alone.  Two  hogs  were  injected  with  disease-producing  blood  alone. 
In  order  to  test  the  likelihood  of  hog  cholera  being  conveyed  tluough 
the  agency  of  vaccinated  hogs,  2  untreated  healthy  hogs  were  placed 
in  each  pen  with  the  serum-simultaneous  vaccinated  hogs,  and  as  a 
control  1  was  placed  in  the  pen  with  the  2  hogs  that  received  disease- 
producing  blood  only. 

Of  the  6  hogs  that  received  10  c.  c.  of  senim  with  disease-producing 
blood,  1  became  sick  and  died,  showing  at  autopsy  the  lesions  of  hog 
cholera.  One  of  the  hogs  that  was  given  20  c.  c.  of  serum  with 
disease-producing  blood  died  nearly  seven  w(»('ks  after  vaccination, 
but  the  symptoms  and  lesions  exhibited  by  this  hog  wen^  sucli  that 
a  positive  diagnosis  of  hog  cholera  could  not  be  made.  The  other 
vaccinated  hogs  remained  well,  as  did  all  of  the  clu'cks  in  the  pens 
with  the  vaccinated  hogs.  Both  of  the  hogs  that  were  given  disease- 
producing  blood  alone  died  of  hog  cholera,  and  their  check  contracted 
the  disease  from  them  and  died. 

All  of  the  surviving  senim-simultaneous  vaccinated  hogs  w(Te 
exposed  to  infection  at  the  same  time,  4  being  placed  in  the  ])asture 


36 


PRODUCTION    OF    IMMUNITY    FROM    HOG    CHOLERA. 


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38  PRODUCTION    OF    IMMUNITY    FROM    HOG    CHOLERA. 

and  6  in  the  Scribner  exposure  pen  fifteen  days  after  vaccination. 
None  of  these  hogs  became  distinctly  sick,  though  hogs  1780  and 
1788,  which  were  exposed  in  the  pasture,  became  unthrifty.  Three 
of  the  hogs  that  survived  the  exposure  in  the  pasture  were  placed 
in  the  Scribner  exposure  pen  two  months  and  twelve  days  after  vac- 
cination in  order  to  further  test  their  immunity.  Of  these  3  hogs  1, 
No.  1780,  finally  died  more  than  three  months  after  vaccination. 
The  only  lesion  of  hog  cholera  found  at  the  autopsy  of  this  hog  was 
a  single  button  ulcer  in  the  cecum.  In  view  of  the  lack  of  acute 
lesions  and  the  unthriftiness  which  preceded  the  last  exposure,  it 
seems  probable  that  this  hog  had  contracted  hog  cholera  before 
being  placed  in  the  Scribner  exposure  pen,  and  indeed  the  unthrifti- 
ness of  this  hog  in  the  pasture  may  have  been  caused  by  a  light 
attack  of  hog  cholera  following  vaccination,  the  one  ulcer  found  at 
autopsy  being  the  only  trace  left  of  that  attack. 

Four  of  the  hogs  that  were  treated  with  serum  alone  were  placed 
in  the  Scribner  exposure  pen  nineteen  days  after  vaccination,  while 
the  remaining  4  were  first  exposed  three  months  and  twenty-one 
days  after  vaccination.  Of  the  first  lot,  2  remained  well,  while  2 
died  of  hog  cholera;  2  checks  exposed  at  the  same  time  died  of  hog 
cholera.  The  amount  of  serum  injected  did  not  seem  to  affect  the 
result  of  this  exposure,  as  one  of  the  survivors  had  received  10  c.  c.  and 
the  other  20  c.  c.  of  serum.  Of  the  4  that  were  first  exposed  three 
months  and  twenty-one  days  after  injection  of  the  serum,  all  died, 
and  the  pen  check  exposed  at  the  same  time  also  died  of  hog  cholera. 
Summary  of  experi-ments  with  serum,  from,  immune  IS  13. 

In  all,  18  hogs  were  treated  by  the  serum-simultaneous  method, 
the  serum  being  used  in  doses  of  5  c.  c,  10  c.  c,  15  c.  c.  and  20  c.  c. 
Of  these,  2  became  sick  and  died,  though  it  was  impossible  to  make 
a  positive  diagnosis  of  hog  cholera  in  the  case  of  one  of  them.  In 
the  case  of  one  other  hog  (1780)  there  is  also  some  doubt  whether 
death  resulted  from  vaccination  or  from  subsequent  exposure  to 
disease,  but  for  convenience  in  summarizing,  and  because  no  symp- 
toms of  illness  were  observed  after  vaccination,  the  death  of  the  hog 
is  counted  as  due  to  exposure. 

To  determine  the  virulence  of  the  disease-pro'ducing  blood  used  in 
the  serum-simultaneous  vaccinations,  4  hogs  were  injected  with  dis- 
ease-producing blood  alone.  All  of  these  became  sick  and  3  died. 
Seven  uninoculated  hogs  were  placed  in  pens  with  the  vaccinated 
hogs,  and  all  remained  well.  Two  similar  unvaccinated  hogs  which 
were  placed  in  pens  with  those  injected  with  disease-producing  blood 
alone  died  of  hog  cholera.  None  of  the  hogs  injected  with  serum 
alone  were  made  sick  by  the  injection. 

In  testing  the  immunity  of  the  treated  hogs,  16  that  were  vacci- 
nated by  the  serum-simultaneous  method  were  exposed  to  hog  cholera 


EXPERIMEKTS   WITH   SERUM   FROM   SCRIBNER   IMMUNES.  39 

from  fifteen  to  nineteen  days  after  vaccination,  and  all  remained 
well  except  1780,  which  became  unthrift3^  Three  of  these  hogs 
which  had  been  exposed  originally  in  the  pasture  were  again  exposed 
by  being  placed  in  the  Scribner  exposure  pen  seventy-three  days 
after  vaccination.  One  of  these  (1780)  finally  died  as  described 
above ;  the  other  2  remained  well. 

Of  8  hogs  that  were  treated  with  serum  alone,  none  became  sick 
from  treatment,  but  6  died  when  exposed  to  infection  from  nineteen 
days  to  three  months  and  twenty-one  days  after  vaccination.  It 
is  worthy  of  note  that  the  2  survivors  were,  with  2  others  that  suc- 
cumbed, exposed  only  nineteen  da^^s  after  vaccination.  Of  7  unvac- 
cinated  check  hogs  exposed  along  with  the  treated  hogs,  6  became 
sick  and  5  died. 

The  following  conclusions  may  be  drawn  from  the  experiments 
with  first  drawing  of  serum  from  immune  1313: 

(1)  Serum  from  immune  1313  was  sufficiently  potent  to  protect 
the  great  majority  of  the  injected  hogs  from  a  fatal  dose  of  disease- 
producing  blood  adminsitered  simultaneously  with  the  serum. 

(2)  Hogs  treated  by  the  serum-simultaneous  method,  even  though 
they  became  slightly  sick,  did  not  convey  the  disease  to  nonimmunes 
by  association. 

(3)  Hogs  vaccinated  by  a  simultaneous  injection  of  serum  and 
disease-producing  blood  remaineil  immune  for  at  least  fifteen  days 
after  vaccination." 

(4)  Immunity  subsequent  to  vaccination  in  hogs  which  received 
the  maximum  dose  of  serum  with  disease-producing  blood  was  quite 
as  firm  as  in  those  that  received  the  minimum  dose  in  the  same 
manner. 

(o)  The  immunity  conferred  by  the  serum  of  hog  1313  when 
administered  alone  in  doses  of  10  c.  c.  and  20  c.  c.  did  not  persist  in 
full  force  for  as  long  as  nineteen  days,  and  at  the  end  of  three  months 
and  twenty-one  days  it  seemed  to  have  completely  disappeared. 

Seri'M  from  Immune  1383  (Slow  Method). 

Experiment  V. — Preliminary  experiment  vith  first  drawiiuj  of  serum. 

This  first  experiment  with  the  first  drawing  of  blood  from  immune 
1383  was  carried  out  in  exactly  the  same  manner  as  the  preliniiiuiry 
experiments  with  the  serum-simultaneous  method,  tiie  scrum  being 
given  in  doses  of  5  c.  c,  10  c.  c,  and  15  c.  c.  Two  hogs  were  injected 
with  disea.se-producing  blood  alone,  and  1  uninoculated  hog  wa.s 
placed  in  each  of  the  four  pens  used  in  this  experiinenl.  Tal)le  8 
shows  that  none  of  the  vaccinated  hogs  Ix'tanu'  sick  after  treatment, 
nor  did  any  of  the  check  iiogs  in  the  same  pens  contract  disease  from 

«Othfr  fxp«Tiiiifnt.s  liavcHhowii  that  iiiuiiunit y  followin^j  scruni-Hiinultaiu-ous  iiijcc- 
tiuns  lasts  much  lunger  than  this. 


40 


PRODUCTION    OF   IMMUNITY   FROM    HOG   CHOLERA. 


>> 


«§       ?g        =5^    5!    ?    ^       ^3. 


EXPERIMENTS   WITH   SERUM    FROM    SCRIBNER   IMMUNES.  41 

them.  Both  of  the  hogs  which  were  injected  with  the  same  dose 
of  the  same  disease-producing  blood  as  that  used  on  the  vaccinated 
hogs  but  wdthout  the  serum,  contracted  hog  cholera  and  died,  and 
the  pen  check  with  these  2  hogs  contracted  hog  cholera  from  them, 
but  recovered. 

The  6  vaccinated  hogs  with  their  3  pen  checks  were  placed  in  the 
quarantine  pasture  and  were  there  accidentally  exposed  to  disease 
about  two  and  one-half  months  after  vaccination;  as  a  result  of  tliis 
exposure  all  3  of  the  checks  died  of  hog  cholera,  while  the  vaccinated 
hogs  remained  well. 

Five  of  the  vaccinated  hogs  had  their  immunity  further  tested 
by  being  placed  in  the  Scribner  exposure  pen  a  little  more  than 
three  and  one-half  months  after  vaccination.  They  again  remained 
well,  although  the  disease  to  which  they  were  exposed  was  quite 
virulent. 

The  protection  afforded  against  a  fatal  dose  of  disease-producing 
blood  by  even  5  c.  c.  of  serum  from  imnuine  1383  was  apparently 
complete.  Instead  of  proceeding  with  a  secondary  experiment  in 
the  usual  manner  it  was  decided  to  determine  the  minimum  amount 
of  this  serum  required  to  protect  against  a  fatal  dose  of  diseased 
blood. 

Experiment  VI. — Second  experiment  with  first  drawing  of  scniin. 

No  hogs  were  injected  with  serum  alone  in  this  experiment,  all 
vaccinations  being  made  by  the  serum-sinmltaneous  method.  The 
doses  of  serum  used  were  reduced  to  2^  c.  c,  5  c.  c,  and  7^  c.  c, 
and  only  1  c.  c.  of  disease-producing  blood  was  used.  This  dose  of 
blood  was  only  half  of  that  heretofore  employed,  but  notwithstand- 
ing this  it  proved  to  be  quite  sufficient  to  infect  unprotected  hogs, 
for  all  of  the  hogs  which  received  1  c.  c.  of  the  disease-producing 
blood  alone  died  of  hog  cholera,  and  the  pen  check  exposed  to  them 
likewise  contracted  the  disease  and  died. 

Of  the  6  vaccinated  hogs,  Nos.  1600  and  1601,  which  received 
only  2h  c.  c.  of  serum  with  the  disease-producing  blood,  became 
slightly  sick  after  vaccination;  the  remaining  vaccinated  hogs 
which  received  larger  doses  of  serum  showed  no  syin])toins  of  dis- 
ea.se,  and  none  of  the  pen  checks  exposed  to  the  vaccinated  hogs 
became  sick.  All  of  the  vaccinated  hogs  witii  tlie  pen  checks  were 
moved  to  the  (piarantine  j)asture  and  were  there  e\])osed  to  iiog 
cholera  approximately  two  months  after  vaccination.  Two  of  the 
3  pen  checks  died  as  a  result  of  this  exposure  and  at  autojKsy  tyi)i(al 
lesions  of  hog  choh'ra  were  found.  The  third  check  evidently  ])os- 
sess<Hl  a  high  degree  of  natural  resistance  to  the  di.sca.sc.  for  it  did 
not  become  distinctly  sick  in  the  pasture  nor  in  the  ex])osure  ])en, 
where  it  was  placed  later. 


4^ 


PRODUCTION    OF   IMMUNITY   FROM    HOG   CHOL^^A. 


EXPERIMENTS   WITH    SERUM   FROM    SCRIBNER    IMMUNES.  45 

Two  of  the  6  vaccinated  hogs  died  while  in  the  quarantine  pasture ; 
the  remaining  4  did  not  become  sick.  From  the  autopsy  findings 
there  seems  to  be  little  room  for  doubt  that  the  death  of  hog  1600,  1 
of  the  2  that  died  in  the  quarantine  pasture,  was  due  to  hog  cholera. 
It  has  been  stated  that  this  hog  showed  symptoms  of  illness  shortly- 
after  vaccination.  If  this  was  due  to  a  mild  attack  of  hog  cholera,  as 
was  probably  the  case,  then  it  is  hardly  conceivable  that  the  hog 
could  have  contracted  hog  cholera  in  the  pasture,  unless  indeed  this  be 
a  rare  instance  of  failure  to  acquire  immunity  through  an  attack  of 
the  disease.  It  seems  to  us  more  likely  that  hog  1600  never  com- 
pletely recovered  from  the  mild  attack  of  hog  cholera  which  followed 
vaccination,  and  that  when  placed  in  the  rather  crowded  quarantine 
pasture  it  succumbed.  The  autopsy  showed  only  the  lesions  which 
are  found  in  the  chronic  type  of  hog  cholera.  The  death  of  hog  1604, 
the  other  vaccinated  animal  which  died  in  the  pasture,  can  not  be 
explained  in  the  same  way,  for  this  hog  did  not  show  s^-mptoms  of  ill- 
ness following  vaccination,  and  its  death,  if  caused  by  hog  cholera,  was 
no  doubt  due  to  a  failure  of  the  vaccine  to  afford  protection  for  two 
months,  the  time  which  intervened  between  vaccination  and  expo- 
sure. The  fact,  however,  that  hog  1603  (treated  in  the  same  man- 
ner as  hog  1604),  hog  1601,  which  received  half  as  much  serum,  and 
hogs  1606  and  1607,  which  received  more  serum,  all  remained  well, 
though  subjected  to  the  same  exposure  as  hog  1604,  points  strongly  to 
the  likelihood  that  the  death  of  hog  1604  was  due  to  unusual  suscepti- 
bility, or  else  to  some  cause  other  than  hog  cholera.  This  latter  possi- 
bility must  not  be  overlooked,  as  the  lesions  found  at  autopsy  were  not 
typical  of  that  disease  and  as  the  conditions  in  the  pasture  were  not 
conducive  to  thriftiness.  Three  of  the  surviving  vaccinated  hogs — 
1601,  1603,  and  1606 — were  later  placed  in  the  Scribner  exposure  pen, 
where  they  again  remained  well. 

Experiments  ^^  and  VI  show  that  the  minimum  amount  of  senim 
from  hog  1383  re(iuired  to  protect  with  certainty  from  a  sinndtanoous 
injection  of  a  lethal  dose  of  disease-producinfj  blood  prol)ably  lies  in 
the  neighborhood  of  .5  c.  c.  for  hogs  weighing  from  30  to  35  pounds. 

ExPERiMKNT  \'\\.-   Seromldrairiiuj  of  strinn  from  iiiiDiiiin  l-is.i. 

It  will  be  remembered  that  l)loo(i  was  drawn  from  each  of  the 
immunesattlifferent  times  after  hyperimnumization,  i)ut  in  the  experi- 
ments heretofore  described  only  serum  from  the  first  drawings  of 
blood  was  used.  In  Experiments  VII  and  VIIT  senini  from  the  sec- 
ond and  third  drawings  of  blood  from  hog  13S3  were  tested,  and 
although  no  atteini)t  was  made  to  determine  accurately  the  jxjtency  of 
this  serum,  dost»s  of  10  c.  c.  were  found  to  give  full  |)rote<tion  from  a 
lethal  dose  of  diseast»-producing  blood. 


44 


PRODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 


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Table  10  shows  that  4 
hogs  vaccinated  by  a  si- 
multaneous inj  ection  of  dis- 
ease-producing blood  and 
the  second  drawing  of  se- 
rum remained  well,  al- 
though 3  checks  which  re- 
ceived the  disease-produc- 
ing blood  alone  all  died  of 
hog  cholera.  In  this  ex- 
periment 2  hogs  were  also 
injected  with  serum  alone. 
These  2  were  placed  in  the 
Scribner  exposure  pen  sev- 
enteen days  after  receiving 
the  serum  injection.  They 
remained  well  there  and 
were  removed  to  the  Sy- 
phax  exposure  pen  four 
weeks  later,  and  here  they 
again  remained  well.  The 
virulence  of  the  disease  to 
which  they  were  exposed  in 
the  Syphax  pen  is  shown 
by  the  death  of  unprotected 
checks  exposed  to  the  same 
infection.  (See  Experiment 
XVI.) 

The  4  hogs  vaccinated 
by  the  serum-simultaneous 
method  were  placed  in  the 
quarantine  pasture,  and 
were  there,  with  a  number 
of  others,  accidentally  ex- 
posed to  infection  approxi- 
mately six  weeks  after 
vaccination.  They  all  re- 
mained well  and  were  trans- 
ferred to  the  Scribner  ex- 
posure pen  three  and  one- 
half  months  after  vaccina- 
tion. No  symptoms  of  dis- 
ease followed  this  second 
exposure. 


EXPERIMENTS  WITH   SERUM   FROM   SCRIBNER   IMMUNES. 


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Experiment  VIII. — Third  draw- 
ing of  serum  from  immune 
1383. 

This  experiment  with  the 
third  draAving  of  serum  was 
conducted  in  the  same  man- 
ner as  the  experiment  with 
the  second  drawing,  except 
that  no  hogs  were  vaccinated 
with  serum  alone.  The  re- 
sults were  in  entire  accord 
with  those  of  Experiment 
VII.  The  4  hogs  vaccinated 
by  the  serum-simultaneous 
method,  the  serum  being 
given  in  doses  of  10  c.  c.  and 
20  c.  c.  remained  perfectly 
well.  The  death  of  the  3 
control  hogs,  1661,  1662,  and 
1663,  shows  the  Aarulence  of 
the  diseased  blood  used  in 
the  experiment.  The  vac- 
cinated hogs  were  exposed 
to  hog  cholera  in  the  quaran- 
tine pasture  six  weeks  after 
vaccination,  and  were  given 
a  later  exposure  in  the  Scrib- 
ner  exposure  pen;  none  of 
them  showed  any  .symptoms 
of  illness  following  either  ex- 
posure. 

Svmmarii  of  t.ipcrimnits  with  xerum 
from  ivnnunc  l-iS-i. 

In  summarizing  t  he  results 
obtained  with  the  serum 
from  immune  13S3,  it  should 
be  noted  first  of  all  that  in 
so  far  as  our  results  inthcate 
there  is  no  (lifference  in  the 
protective  power  of  the  fii-st, 
second,  and  third  drawings, 
although  it  is  true  that  no 
attemj)t  was  made  to  deter- 
mine the  minimum  dose  of 


46  PRODUCTION    OF    IMMUNITY   FROM    HOG    CHOLERA. 

serum  of  the  second  and  third  drawings  required  to  protect  from  a 
fatal  dose  of  diseased  blood. 

In  all,  20  hogs  were  treated  by  the  serum-sinmltaneous  method, 
the  doses  of  sei-um  used  varying  from  2^  c.  c.  to  20  c.  c,  and  the  dose 
of  disease-producing  blood  being  from  1  c.  c.  to  2  c.  c.  to  each  hog. 
At  the  same  time  12  hogs  were  injected  with  equivalent  doses  of  the 
same  disease-producing  blood  alone.  Of  the  20  vaccinated  hogs  only 
1  (1600)  died  from  the  treatment,  and  this  hog  received  but  2^  c.  c. 
of  serum.  Of  the  12  hogs  which  received  the  same  disease-producing 
blood  without  any  serum  all  died. 

In  the  pens  with  the  hogs  vaccinated  by  the  serum-simultaneous 
method,  6  checks  were  used  to  determine  the  likelihood  of  the  disease 
being  transmitted  by  vaccinated  hogs.  None  of  these  checks  became 
sick,  but  of  4  checks  placed  in  the  pens  with  hogs  injected  with 
disease-producing  blood  only,  all  contracted  disease. 

Of  the  19  hogs  which  survived  vaccination  by  the  serum-sinmlta- 
neous method,  all  were  exposed  to  hog  cholera  in  the  quarantine 
pasture  from  six  weeks  to  two  and  one-half  months  after  vaccination. 
Only  1  died  from  this  exposure  (1604),  and,  as  previously  explained, 
we  can  not  be  quite  certain  that  this  death  was  really  due  to  hog 
cholera.  Six  pen  checks,  which  had  remained  well  during  exposure 
to  the  vaccinated  hogs,  were  exposed  in  the  pasture  with  the  vacci- 
nated animals,  and  as  a  result  5  died  of  hog  cholera. 

Only  2  hogs  were  vaccinated  with  serum  alone.  These  were  first 
exposed  to  disease  seventeen  days  after  vaccination  and  remained 
well.  Later  exposure  to  disease  in  the  Scribner  and  Syphax  expo- 
sm-e  pens  did  not  produce  sickness  in  these  hogs. 

From  the  results  of  the  experiments  with  serum  from  hog  1383  we 
may  draw  the  following  conclusions: 

1.  Serum  from  hog  1383,  when  given  in  sufficient  dose,  protects 
nonimmunes  from  an  otherwise  fatal  dose  of  disease-producing  blood 
administered  simultaneously  with  the  serum. 

2.  The  serum  alone  in  doses  of  10  c.  c.  protects  from  infection 
occurring  within  17  days  after  the  administration  of  the  serum. 

3.  Immunity  conferred  by  the  serum-simultaneous  method  lasts 
for  two  and  one-half  months  at  least. 

4.  Hogs  treated  by  the  serum-simultaneous  method,  and  which  are 
not  made  ill  by  vaccination,  do  not  communicate  hog  cholera  to  non- 
immunes by  association. 

5.  The  duration  of  immunity  produced  by  the  serum-simultaneous 
method  of  vaccination  does  not  seem  to  be  shortened  by  increasing 
the  dose  of  the  serum  considerably  above  the  amount  necessary  to 
prevent  the  occurrence  of  a  distinct  reaction. 


EXPERIMENTS   WITH   SERUM   FROM    SCRIBNER   IMMUNES.  -17 

Serum  from  Immune  1403  (Slow  Method). 

Although  two  separate  experiments  were  carried  out  ^^'ith  serum 
from  immune  1403,  very  small  doses  of  serum  were  not  used,  the 
experiments  previously  noted  having  shown  that  except  in  the  case 
of  unusually  potent  serum,  such  as  that  from  immune  1383,  10  c.  c. 
was  as  small  a  dose  as  could  be  relied  upon. 

Experiment  IX. — Preliminary  experiment  with  first  drawing  of  serum  from 

immune  1403. 

In  this  experiment  only  the  serum-simultaneous  method  of  vac- 
ciflation  was  used.  Six  hogs  were  vaccinated,  the  dose  of  serum 
being  10  c.  c,  15  c.  c,  and  20  c.  c.  The  same  amount  of  disease- 
producing  blood,  2  c.  c,  was  used  in  all  cases,  and  controls  were 
inoculated  with  2  c.  c.  of  the  same  disease-producing  blood  alone. 
Only  1  (1553)  of  the  6  treated  hogs  showed  signs  of  sickness  after 
vaccination,  while  all  of  the  hogs  that  were  injected  with  the  disease- 
producing  blood  alone  died  of  hog  cholera.  The  pen  checks  exposed 
to  the  vaccinated  hogs  did  not  become  sick,  although  the  check 
exposed  to  the  hogs  which  received  disease-producing  blood  alone 
contracted  hog  cholera  and  died. 

Several  weeks  after  vaccination  5  of  the  treated  hogs  with  their  3 
pen  checks  were  placed  in  the  quarantine  pasture,  ami  4  of  them  were 
there  exposed  to  hog  cholera  approximately  two  and  one-half  months 
after  vaccination.  It  will  be  remembered  that  this  outbreak  of  disease 
in  the  quarantine  pasture  occurred  about  October  15,  1906,  so  that 
hog  1549,  which  died  September  16  (see  Table  12),  was  not  exposed  to 
hog  cholera  after  vaccination.  Of  the  4  vaccinated  hogs  which  were 
exposed  in  the  pasture,  none  showed  symptoms  of  hog  cholera,  though 
1  became  unthrifty.  All  3  of  the  pen  checks  died  in  the  pasture  and 
at  autopsy  showed  distinct  lesions  of  hog  cholera. 

The  4  vaccinated  hogs  which  survived  this  exposure  were  placed  in 
the  Scribner  exposure  pen  three  and  one-half  months  after  vaccina- 
tion. One  of  these  4  hogs  (1556)  was  urtthrifty  when  placed  in  the 
exposure  pen  and  died  about  two  weeks  after  exj)()sure.  The  autopsy 
did  not  disclose  lesions  of  hog  cholera  and  the  death  was  probably  due 
to  other  causes.  Hog  1552,  another  one  of  those  placed  in  the  Scrib- 
ner exposure  pen,  also  died  a  short  while  after  exposure,  but  did  not 
show  positive  lesions  of  hog  cholera  at  autopsy.  This  hog  when  ex- 
posed was  small  and  unthrifty,  and  while  we  can  not  state  the  cause  of 
death  with  certainty,  there  is  a  strong  probability  that,  as  in  th(>  case 
of  hog  1556,  the  death  was  not  due  to  hog  cholera.  The  other  2 
vaccinated  hogs  remained  well  in  the  exposure  pen. 


48 


PRODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 


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EXPERIMENTS   WITH    SERUM    FROM    SCRIBNER   IMMUNES.  49 

Experiment  X. — Second  experiv^ent  with  first  drawing  of  serum  from  immune  1403. 

In  Experiment  X  12  hogs  were  treated  by  the  serum-simultaneous 
method,  half  of  these  being  given  10  c.  c.  and  the  other  half  20  c.  c.  of 
serum.  Eight  hogs  were  given  serum  alone  in  doses  of  10  c.  c.  and  20 
c.  c,  and  4  hogs  were  given  disease-producing  blood  alone  in  the  same 
dose  as  was  used  for  the  serum-simultaneous  vaccinations.  Checks 
were  placed  in  the  pens  with  both  of  the  serum-simultaneous  lots  of 
hogs  and  also  with  those  injected  with  disease-producing  blood  alone. 
Table  13  shows  that  none  of  the  vaccinated  hogs  became  sick,  nor  did 
they  communicate  disease  to  the  exposed  pen  checks.  All  of  the  hogs 
which  received  disease-producing  blood  alone  died,  and  they  commu- 
nicated hog  cholera  to  the  check  which  was  placed  in  the  pen  with 
them. 

For  the  purpose  of  testing  the  subsequent  immunity  of  the  vacci- 
nated hogs,  these  were  divided  into  two  lots.  One  lot  was  to  be  ex- 
posed to  hog  cholera  within  a  few  weeks  after  vaccination,  while  the 
other  was  not  to  be  exposed  for  several  months.  The  first  lot  was 
exposed  in  the  Scribner  exposure  pen,  4  of  the  hogs  treated  by  serum 
alone  being  placed  there  thirteen  days  after  vaccination.  These 
were  followed  eleven  days  later  by  6  of  those  treated  by  the  serum- 
simultaneous  method  (see  Table  13)  and  1  of  the  pen  checks.  This 
pen  check  died  of  hog  cholera;  1  of  the  hogs  vaccinated  with  serum 
alone  became  very  slightly  sick,  but  recovered.  The  other  vaccinated 
hogs  remained  well,  but  in  order  to  secure  further  data  concerning 
the  behavior  of  hogs  immune  from  one  strain  of  disease  when  ex- 
posed to  another  all  of  these  vaccinated  hogs  were  later  placed  in 
the  Syphax  exposure  pen,  where  they  all  remained  well. 

The  other  lot  of  vaccinated  hogs  in  this  experiment,  -with  2  checks, 
was  placed  in  the  quarantine  pasture  and  there  exposed  to  hog 
cholera  seven  weeks  after  vaccination.  Both  checks  contracted  hog 
cholera;  one  died,  and  the  other  was  killed  when  in  a  moribund  con- 
tion,  and  at  autopsy  showed  typical  lesions  of  that  disease.  One  of 
the  hogs  (1638)  treated  with  serum  alone  also  became  sick  following 
this  exposure  and  died  of  hog  cholera,  as  did  hog  1628,  which  was 
treated  with  20  c.  c.  of  serum  plus  2  c.  c.  of  disease-producing  blood. 
None  of  the  other  vaccinated  hogs  became  sick,  and  all  of  them, 
except  hog  1620,  which  was  unthrifty,  were  placed  in  the  Scribner 
exposure  pen  about  four  months  after  vaccination.  None  of  them 
contracted  hog  cholera  from  this  exposure. 

Summary  of  experiments  with  serum  from  immune  l-if>.i. 

Only  the  first  drawing  of  .senim  was  used.  In  nil  IS  hogs  were 
treated  by  the  serum-sinudtaneous  method,  the  doses  of  serum  given 
in  conjunction  with  2  c,  c.  of  di.sease-producing  blotxl  being  10  c.  c, 

12840— No.  102—08 1 


50 


PRODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 


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TESTS    OF    SERUM    FROM    SYPHAX    IMMUNES.  51 

15  c.  c,  and  20  c.  c.  Of  these  18  hogs  1  became  sUghtlv  sick  as  a 
result  of  vaccination  but  soon  recovered,  while  the  others  remained 
well.  As  controls  on  the  virulence  of  the  disease-producinor  blood, 
as  well  as  on  the  protective  power  of  the  serum,  7  hogs  were  injected 
with  disease-producing  blood  alone  in  the  same  dose  as  that  given  the 
vaccinated  hogs.  All  of  these  controls  died  of  hog  cholera.  To  test 
the  danger  of  vaccinated  hogs  convej^ng  the  disease  to  nonimmunes, 
6  checks  were  exposed  in  the  pens  with  those  treated  by  the  serum- 
simultaneous  method.  None  of  these  checks  became  sick,  although 
the  2  checks  exposed  to  hogs  injected  with  disease-producing  blood 
alone  contracted  hog  cholera,  as  was  to  be  expected. 

Of  the  18  hogs  treated  by  the  serum-simultaneous  method  which 
were  exposed  to  infection  at  various  times  after  vaccination,  1  con- 
tracted hog  cholera  and  died ;  none  of  the  others  became  sick. 

Of  8  hogs  treated  with  the  serum  alone,  1  contracted  hog  cholera 
when  exposed  seven  weeks  after  vaccination;  the  others  remained 
well. 

Of  6  unvaccinated  hogs  exposed  along  with  the  treated  animals, 
all  died  of  hog  cholera. 

These  experiments  warrant  the  following  conclusions: 

(1)  Serum  from  immune  1403  when  given  in  sufficient  doses  affords 
perfect  protection  from  an  otherwise  fatal  dose  of  disease-producing 
blood  administered  simultaneously. 

(2)  Hogs  vaccinated  by  the  serum-simultaneous  method,  \nth  rare 
exceptions,  remain  immune  for  at  least  seven  weeks  after  vaccination. 

(3)  Hogs  treated  by  the  serum-simultaneous  metiiod,  if  not  made  ill 
by  the  treatment,  do  not  convey  hog  cholera  to  others  by  association. 

(4)  For  seven  weeks  after  vaccination  innnunity  in  hogs  treated 
with  serum  alone  is  as  firm  as  in  those  treated  by  tiie  serum-simul- 
taneous method. 

(5)  Hogs  immunizetl  from  one  strain  of  hog  cholera  an-  also  im- 
mune from  other  strains  of  the  same  (Hsease. 

TESTS    OF    SEUIM     FROM     HOGS    H YPERIMM UM/.KD     Wnil     BLOOD    FROM 
THE  SYI'MAX  OITBRE.VK. 

SkKIM    KUO.M     ImMI   NK     l.'i'.tli    ((^l  UK    MkTUOI)). 

ICxTKiiiMKNT  XI.  —  First  ilrduimi  o/.siniin. 

The  resuhs  (>l)tain<Hl  in  KxpcrinuMit  XI  iHd  not  (hlTcr  materially 
from  those  of  similar  experiments  carried  out  with  .serum  from  iin- 
numes  treateil  with  the  Scribner  ilisea.s('-i)ro(luciMg  i)lood.  The 
smallest  do.se  of  serum  used  was  10  c.  c,  and  although  the  2  hogs 
given  this  dose  did  not  Ix'come  visii)ly  sick  from  the  serum-siuuil- 
taneous  vaccination,  the  fact  that  1  of  tho.se  given  1.')  c.  c.  as  well  as  1 


52 


PRODUCTION    OF    IMMUNITY   FROM    HOG    CHOLERA. 


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TESTS    OF    SERUM    FROM    SYPHAX    IMMUNES. 


53 


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54  PRODUCTION    OF    IMMUNITY   FROM    HOG    CHOLERA. 

given  20  c,  c.  of  serum  did  become  sick  makes  it  quite  probable  that 
less  than  10  c.  c.  of  this  serum  could  not  be  used  ^vith  2  c.  c.  of  virulent 
blood  with  safety.     (See  Table  14.) 

None  of  the  hogs  treated  by  the  serum-simultaneous  method  died, 
although  2  became  sick,  as  already  stated;  notwithstanding  the  sick- 
ness of  the  2  vaccinated  hogs,  the  untreated  pen  checks  exposed  to 
them  did  not  become  sick.  Both  of  the  hogs  injected  with  disease- 
producing  blood  alone  became  sick  and  died  of  hog  cholera,  and  they 
also  communicated  disease  to  their  pen  check. 

Following  out  the  usual  plan,  the  surviving  hogs  from  this  experi- 
ment were  placed  in  the  quarantine  pasture.  These  hogs  had  been 
vaccinated  two  months  when  the  accidental  outbreak  of  disease 
occurred  in  the  pasture,  but  none  of  them  became  sick  from  the 
exposure.  Two  of  the  3  checks  which  were  placed  in  the  pasture 
with  the  treated  animals  died  of  hog  cholera ;  the  tliird  check  became 
unthrifty  and  died,  but  apparently  did  not  suffer  from  hog  cholera. 
Four  of  the  vaccinated  hogs  were  later  transferred  to  the  Scribner 
exposure  pen  and  again  remained  well. 

Experiment   XII. — Second  experiment  irith  first  drawing  of  serum  from  immune  1,392. 

In  Experiment  XII  12  hogs  were  treated  by  the  serum-simultane- 
ous method,  8  were  treated  with  serum  alone,  and  2  were  injected 
with  disease-producing  blootl  alone.  Four  uninoculated  hogs  were 
placed  in  the  pens  wath  the  serum-simultaneous  hogs,  and  1  with  the 
2  that  received  disease-producing  blood  only.  As  a  result  of  the 
treatment,  as  far  as  could  be  observed  none  of  the  vaccinated  hogs 
showed  symptoms  of  illness,  and  the  checks  in  the  pens  with  them 
also  remained  well.  With  the  hogs  that  received  disease-producing 
blood  alone  the  result  was  quite  different,  for  both  contracted  hog 
cholera  and  one  died;  the  pen  check  that  was  exposed  to  these  hogs 
also  became  sick  and  died  of  hog  cholera.     (See  Table  15.) 

For  the  purpose  of  testing  the  immunity  possessed  by  the  vacci- 
nated hogs  at  different  lengths  of  time  after  vaccination,  these  hogs 
were  divided  into  two  lots,  6  of  the  serum-simultaneous  vaccinated 
hogs  being  placed  in  the  Syphax  exposure  pen  seventeen  days  after 
vaccination  and  4  of  the  hogs  treated  with  serum  alone  in  the  same 
pen  eleven  days  after  vaccination.  Table  15  shows  the  results  of 
these  exposures.  Of  the  6  hogs  treated  by  the  serum-simultaneous 
method  and  exposed  seventeen  days  after  vaccination,  all  remained 
well;  of  the  4  hogs  vaccinated  with  serum  alone  and  exposed  in  the 
Syphax  exposure  pen  eleven  days  after  .vaccination,  1  (1704),  after 
being  sick  a  long  time,  died  about  two  months  later,  probably  of  hog 
cholera,  although  the  lesions  fountl  at  autopsy  were  slight  and  not 
such  as  would  be  expected  from  a  chronic  case  of  hog  cholera.  The 
other  3  hogs  (1703,  1706,  and  1708),  vaccinated  with  serum  alone, 


TESTS    OF    SERUM    FROM    SYPHAX    IMMUNES.  -       55 

remained  well  and  were  later  exposed  to  the  Scribner  disease  without 
being  made  sick.  Two  of  the  uninoculated  check  hogs  were  placed 
in  the  exposure  pen  with  the  serum-simultaneous  hogs,  and  both 
died  of  hog  cholera. 

The  exposure  of  the  second  lot  of  hogs  in  this  experiment  took 
place  in  the  quarantine  pasture  thirty  days  after  vaccination.  Of 
the  6  serum-simultaneous  hogs  that  were  exposed  there,  1  (1696) 
did  not  thrive,  and  finally  died  of  hog  cholera  seven  weeks  after  vac- 
cination, while  the  others  remained  well.  The  death  of  hog  1696 
was  probably  due  to  a  mild  form  of  disease  caused  by  the  origmal 
serum-simultaneous  vaccination,  as  the  hog  at  autopsy  showed  the 
lesions  of  the  chronic  type  of  hog  cholera,  though  it  had  been  exposed 
to  disease  in  the  pasture  only  three  weeks  at  the  time  of  its  death. 
Of  the  4  hogs  treated  with  serum  alone,  which  were  accidentally 
exposed  in  the  quarantine  pasture  thirty  days  after  vaccination,  1 
(1707)  died  of  hog  cholera.  The  others  did  not  contract  the  disease. 
Both  of  the  pen  checks  that  were  placed  in  the  pasture  with  the 
vaccinated  hogs  died  of  hog  cholera. 

Summary  of  experiments  with  serum  from  immune  1S92. 

A  summary  of  the  results  obtained  through  the  use  of  the  first 
drawing  of  serum  from  immune  1392  shows  that  of  18  hogs  treated 
by  the  serum-simultaneous  method,  the  serum  being  used  in  doses  of 
10  c.  c,  15  c.  c,  and  20  c.  c,  1  became  sick  and  1  (1696;  see  above) 
died  from  the  treatment.  Of  4  hogs  injected  with  the  same  amount 
of  the  same  disease-producing  blood  as  that  used  for  the  serum- 
simultaneous  treatment,  all  became  sick  and  3  died. 

All  of  the  surviving  treated  hogs  with  the  survi\nng  checks  were 
exposed  to  infection  after  vaccination.  All  17  of  the  serum-simulta- 
neous hogs,  exposed  seventeen  to  thirty  days  after  vaccination,  re- 
mained well;  2  of  the  8  hogs  treated  with  serum  alone  died  of  hog 
cholera  when  exposed  eleven  to  thirty  days  after  treatment,  while  of 
4  checks  exposed  in  the  same  manner  as  the  treated  hogs,  all  liied  of 
hog  cholera. 

As  a  result  of  these  experiments  it  will  be  seen  that— 

(1)  The  serum  of  hog  1392,  in  doses  of  10  c.  c.  or  more,  was  sufficient 
to  protect  hogs  from  a  fatal  dose  of  disease-producing  blood  a(hnin- 
Lstered  simultaneously  with  the  serum. 

(2)  Hogs  treat<»(l  by  simultaneous  injections  of  sennn  from  hog 
1392,  together  with  disease-producing  blood,  remained  imnuine  for  at 
least  thirty  days  aft<'r  vaccination. 

(3)  Hogs  treated  by  the  senim-simultaneous  method,  cvoii  whrn 
they  became  distinctly  sick,  did  not  convey  disease  to  unprotected 
animals  which  associated  with  them. 


56 


PRODUCTION    OF   IMMUNITY   FROM   HOG   CHOLERA. 


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TESTS   OF   SERUM   FROM   SYPHAX   IMMUNES.  57 

(4)  The  immunity  produced  by  injections  of  serum  alone  from  hog 
1392  did  not  seem  to  be  as  complete  as  that  produced  by  a  simulta- 
neous injection  of  serum  and  disease-producing  blood. 

(5)  Hogs  immunized  with  serum  prepared  through  the  use  of  one 

strain  of  disease  were  immune  when  exposed   to  another  strain  of 

disease. 

Serum  from  Immune  1274  (Quick  Method). 

Experiment  XIII. — Preliminary  experiment  toith  first  drawing  of  serum. 

The  preliminary  experiment  with  the  first  drawing  of  serum  from 
immune  1274  consisted  of  serum-simultaneous  vaccinations  only,  a 
certain  number  of  controls  being,  of  course,  used.  The  results  of  this 
experiment  were  not  entirely  successful,  as  may  be  seen  from  Table  16. 

First  of  all,  we  find  that  serum  from  hog  1274  probably  has  distinct 
protective  power  when  injected  simultaneously  with  a  fatal  dose  of 
disease-producing  blood.  This  is  indicated  by  the  death  of  the  2  hogs 
that  received  disease-producing  blood  alone,  and  the  survival  of  all 
those  treated  with  serum.  At  the  same  time  it  is  surprising  that  the 
2  hogs  that  received  10  c.  c.  of  serum  with  the  disease-producing  blood 
should  have  become  distinctly  sick,  whereas  the  2  that  received  only 
5  c.  c.  of  serum  remained  well.  This  result  could  only  be  explained 
on  the  ground  of  unusual  susceptibility  on  the  part  of  hogs  1718  and 
1719,  or  because  hogs  1715  and  1716,  which  received  only  5  c.  c.  of 
serum,  were  exceptionally  resistant  to  the  disease.  In  the  light  of  this 
experiment  only,  the  latter  supposition  seems  to  be  the  most  reason- 
able explanation  of  the  conflicting  results,  for  when  the  vaccinated 
hogs  with  their  pen  checks  were  exposed  to  hog  cholera  in  the  (juaran- 
tine  pasture  three  weeks  after  vaccination  only  one  of  the  tliree  pen 
checks  (1723)  died  of  hog  cholera.  It  is  tnie  that  one  other  sickened, 
but  it  recovered,  and  the  third  check  never  became  distinctly  sick  in 
the  quarantine  pasture.  The  subsecjuent  death  of  this  check  (1717) 
in  the  exposure  pen  can  not  be  attributed  to  hog  cholera.  It  appears, 
therefore,  that  the  lot  of  hogs  used  in  this  experiment  taken  as  a  whole 
were  probably  more  than  normally  resistant  to  hog  cholera,  and  ft)r 
this  reason  too  great  stress  shoukl  not  be  laid  upon  the  results.  At 
the  .same  time  the  serum  must  have  given  the  vaccinated  hogs  a  cer- 
tain degree  of  protection,  for  both  of  the  controls  injected  with  di.s- 
ea.se-producing  blood  alone  became  very  sick,  one  of  them  died,  and 
the  other  was  killed  to  secure  blood  for  other  experiments,  and  at 
autopsy  both  showed  characteristic  lesions  of  hog  choh'ra.  In  con- 
trast to  this  is  the  behavior  of  the  hogs  which  received  the  same  (h.s- 
ease-producing  blood  in  comi)ination  with  the  serum,  not  one  of 
these  having  died  from  vaccination,  ^\^len  this  lot  of  hogs  was  ex- 
posed to  disease^  in  the  (|uarantine  pasture  one  of  the  pen  checks  died 
of  hog  cholera,  one  became  sick  but  recovered,  while  the  other  n«»ver 
showed  marked  symptoms  of  illness.  With  regard  to  the  tnMited 
hogs  in  the  (juarantine  pasture,  we  find  that  one  of  thos<»  which  had 


58 


PRODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 


received  but  5  c.  c.  of  serum  with  the  disease-producing  blood  died, 
but  a  positive  diagnosis  of  hog  cholera  could  not  be  made  from  the 
autopsy  findings.  The  2  hogs  that  were  made  sick  by  vaccination 
remained  more  or  less  unthrifty,  but  neither  contracted  hog  cholera; 
the  other  3  vaccinated  hogs  remained  well  in  the  quarantine  pasture 
as  well  as  in  the  Syphax  exposure  pen  where  they  were  placed  after 
removal  from  the  pasture. 

Experiment  XIV. — Second  experiment  with  first  drawing  of  sentvi  from  immune  1274- 

The  second  experiment  with  serum  from  hog  1274  is  incomplete, 
as  the  vaccinated  hogs  were  not  exposed  to  natural  infection  after 
vaccination.  The  results  of  the  vaccination  are  of  interest,  how- 
ever, for  comparison  with  those  of  the  preceding  experiment  in  which 
the  2  hogs  treated  by  the  serum-simultaneous  method  with  10  c.  c. 
of  serum  became  distinctly  sick.  In  Experiment  XIV  none  of  the 
12  hogs  which  were  given  serum  with  disease  producing  blood  became 
sick,  although  both  of  the  hogs  treated  with  the.  blood  alone  died  of 
hog  cholera.  Owing  to  the  lateness  of  the  season  and  to  the  fact  that 
our  plans  to  hold  vaccinated  hogs  for  several  months  before  exposing 
them  had  been  interfered  with  considerably  by  the  accidental  out- 
break of  hog  cholera  in  our  quarantine  pasture,  it  was  decided  to 
reserve  all  of  the  vaccinated  hogs  in  Experiment  XIV,  together 
with  their  pen  checks,  for  exposure  during  the  summer  of  1907. 


Table 

17. — Secondary  experiment  with  first  drawing  of  serum  from  hog  1274  {"quick"- 
immune — Syphax). 

No.  of 

Weight. 

Material  injected. 

Inoculation. 

Remarks. 

hog. 

Date. 

Result. 

1938.... 
1939 

Pounds. 
55 

50 
70 
45 
40 
40 
40 

40 
50 
40 
40 
75 
75 
40 
50 
60 
50 
80 
75 
40 
40 

40 
40 

40 
30 

70 

40 

10  c.  c.  serum  and  2  c.  c.  dis- 
ease-producing  blood    of 
hog  1925. 

Dee.   20,1906 
do 

Remained  well 

do 

Not  exposed. 
Do. 

1940.   .. 

do 

do 

do 

do 

do 

do 

do 

do 

Do. 

1941  ... 

do 

do 

Do. 

1942 

do 

do 

Do. 

1943 

...do     .                         

do 

Do. 

1946.... 
1947.... 

20  c.  e.  serimi  and  2  c.  c.  dis- 
ease-producing blood    of 
hog  1925. 

do 

do 

Do. 
Do. 

1948 

do 

do 

..do 

Do. 

1949 

do 

do 

do 

Do. 

1950 

do 

do 

do 

Do. 

1951.... 

do 

do 

do 

Do. 

1954  ... 

10  c.  c.  serum  alone 

do 

.  ..do 

Do. 

1955 

do : ,. 

do 

....do 

Do. 

1956 

do 

do 

do 

Do. 

1957  . 

..do 

do 

.do 

Do. 

1958 

20  c.  c.  serum  alone 

do 

do 

Do. 

1959 

do 

do 

do 

Do. 

I960.... 

do 

do 

do 

Do. 

1961 

..do 

do 

.    .do 

Do. 

1944 

Pen  check  with  hogs  1938  to 

1943. 
.     ..do 

do 

Do. 

1945 

.do 

Do. 

1952.... 

Pen  check  with  hogs  1946  to 

1951. 
..  ..do 

do 

Do. 

1953 

.do 

Do. 

1962. . . . 
1963.... 
1964. . . . 

2    c.    c.    disease-producing 

blood  of  hog  1925. 
do 

Pen  check  with  hogs  1962 
and  1963. 

Dec.  20,1906 
do 

Sick    Dec.    27,    1906; 

died  Jan.  3, 1907. 
Sick    Dec.    27,    1906; 

died  Jan.  7, 1907. 
Sick    Jan.     8,     1907; 

died  Jan.  12, 1907. 

Hemorrhages. 

Do. 
Hemorrhages 

and  ulcers. 

TESTS    OF    SERUM    FROM    SYPHAX    TMMUNES,  59 

Summary  of  results  obtained  with  first  drawing  of  serum  from  immune  1274. 

Eighteen  hogs  were  vaccinated  by  the  serum-simultaneous  method, 
serum  in  doses  of  5  c.  c,  10  c.  c,  15  c.  c,  and  20  c.  c.  being  used  in  con- 
junction with  2  c.  c.  of  disease-producing  blood.  Of  these  18  hogs  2 
became  sick;  none  died. 

Four  hogs  were  injected  with  disease-producing  blood  alone;  aU 
became  sick;  3  died,  and  1  was  killed  when  in  a  moribund  condition. 

Eight  hogs  were  injected  wath  serum  alone  and  all  remained  well. 

Only  6  of  the  vaccinated  hogs  were  later  exposed  to  infection;  1  of 
these  died,  but  without  exhibiting  either  before  death  or  at  autopsy 
positive  signs  of  hog  cholera.  Of  3  pen  checks  which  were  exposed  at 
the  same  time  as  the  6  vaccinated  hogs,  1  died  of  hog  cholera,  the 
other  became  sick  but  recovered,  while  the  third  check  did  not  become 
plainly  ill. 

As  a  result  of  the  experiments  with  the  first  drawing  of  serum  from 
hog  1274,  we  may  conclude  that — 

(1)  The  serum  when  given  in  sufficient  dose  will  protect  non- 
immunes from  a  simultaneous  injection  of  a  fatal  dose  of  disease- 
producing  blood. 

(2)  The  serum-simultaneous  injections  in  which  the  largest  dose  of 
hyperimmune  serum  was  used  seemed  to  afford  quite  as  com})lete 
protection  from  hog  cholera  when  exposure  took  place  three  weeks 
after  vaccination  as  was  afforded  by  the  injection  of  disease-producing 
blood  with  a  smaller  dose  of  serum. 

(3)  An  insufficient  dose  of  serum  with  disease-producing  blood  ap- 
peared to  result  in  more  or  less  permanent  injury  to  tlie  hogs  treated 
in  that  manner. 

Seri'm  from  Immune  1297  {Si,o\v  Method). 

Experiment  XV. —  First  drnirimj  of  nerum. 

The  preliminary  experiment  with  tlie  senim  from  immune  1207 
shows  that  5  c.  c.  of  that  senim  was  not  sufficient  to  in.suro  ])roteotion 
from  a  fatal  dose  of  disease-producing  blood  administered  with  the 
senim,  for,  as  may  be  seen  from  Tal)le  IS,  hog  1742  died  of  hog  cholera 
after  vaccination.  The  other  liog  injected  in  the  same  manner  as  hog 
1742,  however,  remained  well,  as  did  the  ])en  check  that  associated 
^ith  these  two  hogs.  None  of  the  hogs  treated  with  doses  of  10  c.  c. 
and  lo  c.  c.  of  serum  plus  di.sease-producing  blood  showed  any  .>^ymj)- 
toms  of  illness,  but  both  of  the  hogs  that  received  di.sease-producing 
blood  alone  became  sick,  and  one  of  them  died.  The  pen  check  that 
was  exposed  to  the  hogs  that  were  injected  with  di.sease-prodiicing 
blood  alone  ccmtracted  hog  cholera  from  them  and  died.  With  the 
exception  of  hogs  174.'i  and  1744.  all  of  the  .surviving  vaccinated  hogs 
with  their  ])en  checks  were  j)lace(l  in  the  pasture  on  October  17  to 


60 


PRODUCTION    OF   IMMUNITY   FROM    HOG    CHOLERA. 


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TESTS    OF    SERUM    YROM    SYPHAX    IMMUNES.  61 

await  future  exposure.  The  accidental  outbreak  of  hog  cholera  in 
this  pasture  made  its  appearance  about  the  time  that  the  hogs  were 
placed  there,  and  they  may  therefore  be  regarded  as  having  been 
exposed  to  disease  on  October  17,  or  twenty-two  days  after  vacci- 
nation. Both  pen  checks  that  were  exposed  at  the  same  time  with  the 
vaccinated  hogs  became  sick;  one  died,  but  the  other  recovered. 
None  of  the  4  treated  pigs  became  sick  in  the  pasture,  and  during  a 
subsequent  exposure  in  the  Scribner  exposure  pen  they  likewise 
remained  well.  Hogs  1743  and  1744,  one  a  vaccinated  hog  and  the 
other  a  pen  check,  were  placed  on  October  29,  1906,  in  a  separate 
pasture  that  was  used  for  hogs  that  had  been  made  sick  by  vaccin- 
ation or  that  had  been  removed  from  the  exposure  pen.  Athough 
there  was  undoubtedly  ample  opportunity  for  these  hogs  to  contract 
hog  cholera  in  this  pasture,  neither  of  them  did  so,  but  hog  1743  was 
killed  by  other  hogs.  The  pen  check  1744  was  placed  in  the  Scribner 
exposure  pen  on  January  23,  1907,  to  further  test  its  immunity,  with 
the  result  that  it  survived  without  showing  disease. 

Experiment  XVI. — Second  experiment  with  first  drauing  of  serum. 

In  the  second  experiment  with  serum  from  immune  1 297  the  usual 
plan  was  followed.  Twelve  hogs  were  treated  by  the  serum-simulta- 
neous method,  6  of  them  being  given  10  c.  c.  of  serum,  and  6,  20  c.  c. 
of  serum  with  2  c.  c.  of  disease-producing  blood  in  each  case;  4  hogs 
were  injected  with  10  c.  c.  of  serum  alone  and  4  with  20  c.  c.  of  senim 
alone;  2  hogs  were  injected  with  2  c.  c.  of  the  disease-producing  blood 
alone.  Two  uninoculated  checks  were  placed  in  the  pens  with  each 
of  the  lots  treated  by  the  senim-simultaneous  method,  and  1  was 
placed  in  the  pen  with  the  hogs  that  were  injected  with  disease-pro- 
ducing blood  alone.  As  may  be  seen  from  Table  19,  all  of  the  animals 
that  were  injected  \vith  senim  alone  or  with  serum  and  disease-pro- 
ducing blood  combined,  together  with  their  pen  checks,  remained  well 
after  treatment.  Both  of  the  hogs  that  were  injected  with  disease- 
producing  blood  alone  contracted  hog  cholera,  and  their  pen  check 
contracted  the  disease  from  them  and  died  of  hog  cholera. 

In  order  to  test  further  the  immunity  of  the  vaccinated  hogs,  lialf 
of  those  vaccinated  by  the  serum-simultaneous  method,  together  with 
half  of  those  treated  with  serum  alone,  were  plac<Ml  in  the  Scribner 
expo.sure  pen  three  weeks  after  vaccination.  All  4  of  the  surviving 
pen  checks  were  exposed  at  practically  th<'  same  time.  The  s(>rum- 
simultaneous  vaccinated  hogs  all  remained  well  as  a  result  of  this 
exposure,  but  3  of  the  4  hogs  treated  with  s(>rum  alone  died  of  hog 
cholera,  and  3  of  the  4  untreated  check  hogs  also  died. 

The  other  treat«'(l  hogs  that  were  not  exposed  with  the  lot  just 
described  were  exposed  as  follows:  Five  hogs  treated  by  the  serum- 
simultaneous  method  were  expo.sed  in  the  Scribner  exj)<)sure  pen 
iifty-one  days  after  vaccination.     Four  hogs  that  were  treated  with 


62 


PRODUCTION    OF   IMMUNITY   FROM   HOG   CHOLERA. 


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TESTS    OF    SERUM    FROM    SYPHAX    IMMUNES.  63 

serum  alone  were  exposed  in  the  same  pen  tw  elve  weeks  after  vacci- 
nation. The  virulence  of  the  disease  to  which  the  serum-simultane- 
ous treated  hogs  were  subjected  is  shown  by  the  fact  that  7  check 
hogs  (1992-1998,  Table  19)  placed  in  the  exposure  pen  five  days  later 
all  died  of  hog  cholera,  but  notwithstanding  this  very  severe  test,  all 
of  the  serum-simultaneous  vaccinated  hogs  remained  well.  Of  the  4 
hogs  vaccinated  with  serum  alone  and  exposed  twelve  weeks  after 
treatment  3  died,  as  was  to  be  expected,  since  the  hogs  treated  simi- 
larly and  exposed  only  three  weeks  after  treatment  did  not  show  any 
appreciable  degree  of  resisting  power. 

Summary  of  results  obtained  with  serum  from  immune  1297. 

Eighteen  hogs  were  vaccinated  by  the  serum-simultaneous  method, 
the  serum  being  used  in  doses  of  from  5  c.  c.  to  20  c.  c.  Only  1  of 
these  hogs  died  from  the  treatment,  and  this  hog  (1742)  received  but 
5  c.  c.  of  the  serum.  Four  hogs  were  injected  with  the  same  dose  of 
the  same  disease-producing  blood  as  was  given  the  serum-simultane- 
ous treated  hogs,  and  as  a  result  all  became  sick  and  3  died.  Of  6 
pen  checks  exposed  to  the  serum-simultaneous  treated  hogs  after  vac- 
cination all  remained  well,  although  both  of  the  checks  exposed  to 
hogs  treated  with  diseased  blood  alone  contracted  hog  cholera  and 
died. 

In  regard  to  immunity  in  the  treated  hogs  subsequent  to  vaccina- 
tion it  is  seen  that  of  the  16  serum  simultaneous  treated  hogs  all 
remained  well  when  exposed  from  three  to  seven  weeks  after  vaccina- 
tion. Of  8  hogs  treated  with  serum  alone  and  exposed  to  hog  cholera 
from  three  to  twelve  weeks  after  vaccination  we  find  that  6  died  of 
hog  cholera,  while  of  4  checks  not  inoculated  and  exposed  to  the  same 
infection  3  died. 

With  regard  to  the  experiments  with  the  first  drawing  of  serum 
from  imnume  1297,  the  following  conclusions  may  be  drawn: 

(1)  When  administered  in  sufTicient  dose  this  serum  will  com- 
pletely protect  hogs  from  an  otherwi.se  fatal  dose  of  disease-producing 
blood  given  simultaneously  with  the  .serum. 

(2)  The  innnunity  produced  by  a  serum-sinudtaneous  vaccination 
remained  (|uite  firm  for  at  least  seven  weeks. 

(3)  This  innnunity  was  (piite  as  firm  in  the  hogs  that  received  20 
c.  c.  of  senim  Avith  disease-producing  blood  as  in  tlio.se  that  received 
only  10  c.  c. 

(4)  It  is  not  necessary'  for  hogs  to  show  visible  symptoms  of  illness 
after  vaccination  in  order  to  secure  innnunity  that  will  last  at  least 
seven  weeks. 

(5)  The  imnuinity  in  .s<»nnn-sinniltaneous  vaccinated  hogs  was  not 
due  to  serum  alone,  as  shown  by  the  death  of  animals  injected  with 
serum  alone  when  exposed  to  hog  cholera. 


64 


PRODUCTION   OF   IMMUNITY   FROM   HOG   CHOLERA. 


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TESTS    OF   SERUM   FKOM    SYPHAX   IMMUNES.  65 

(6)  Hogs  inimunized  with  serum  prepared  from  one  strain  of  dis- 
ease (Sj^hax)  may  be  expected  to  resist  infection  of  the  same  nature 
from  an  entirely  different  source  (Scribner). 

(7)  Hogs  vaccinated  by  the  serum-simultaneous  method,  if  not 
made  sick  by  the  treatment,  ^^'ill  not  communicate  disease  to  other 
hogs. 

Sertm  from  Immine  1310  (Slow  Method). 
Experiment  XVII. — Preliminary  experiment  icith  first  dravinej  of  serum. 

In  this  experiment  only  the  serum-simultaneous  method  of  vacci- 
nation was  used,  and  Table  20  shows  the  results.  Six  hogs  were  vac- 
cinated by  the  serum-simultaneous  method,  doses  of  5  c,  c,  10  c.  c, 
and  15  c.  c.  of  serum  being  used.  Of  the  4  hogs  injected  with  less 
than  15  c.  c.  of  serum  all  became  sick  and  2  died,  and  the  2  pen  checks 
contracted  hog  cholera  from  them.  The  2  hogs  that  were  injected 
with  15  c.  c.  of  serum  in  combination  with  the  disease-producing 
blood  remained  well,  while  the  2  injected  with  disease-producing  blood 
alone  died  and  communicated  disease  to  their  pen  check. 

Three  of  the  sursaving  vaccinated  hogs  in  this  experiment  were 
exposed  to  hog  cholera  in  the  quarantine  pasture  and  1  in  the  Syphax 
exposure  pen.  It  was  to  be  expected  that  the  hogs  that  had  been 
sick  would  be  subsequently  immune,  and  this  was  found  to  be  the  case. 

The  chief  interest  in  the  exposure  of  these  hogs  lay  in  the  behavior 
of  the  hogs  that  received  15  c,  c.  of  serum  with  disease-producing  blood 
and  which  did  not  become  ill  as  a  result  of  vaccination.  These  2  hogs 
(1677  and  1678)  were  exposed  to  hog  cholera  in  the  })asture  thirty- 
seven  days  after  vaccination.  They  ditl  not  become  sick  as  a  result  of 
this  exposure,  although  their  pen  check  which  was  exposed  with  them 
contracted  hog  cholera  and  died.  A  later  exposure  of  these  2  hogs  in 
the  Scribner  exposure  })en  three  and  one-half  months  after  vaccination 
proved  them  to  be  still  immune. 

ExPEKiMKNT  Will.     Second  experiment  irilli  frst  drauinrj  of  serum. 

In  this  experiment,  through  an  error,  doses  of  10  c.  c.  and  20  c.  c. 
of  senun  were  used  with  disease-prockicing  blood,  altliough  tlie  prelim- 
inary exjx'riment  had  shown  that  10  c.  c.  of  this  serum  was  not 
sulhcient  to  j)rotect  hogs  from  a  fatal  dose  of  (lisease-j)r()(lucing  hlood. 
It  api>ears,  however,  that  even  the  dose  of  10  c.  c.  of  serum  may  have 
increjised  the  resisting  j)ower  of  the  vaccinated  hogs  somewhat.  Six 
hogs  were  injected  with  10  c.  c.  of  serum  |)lus  (lisease-|)ro(lu(ing  i)loo(l, 
(■)  with  20  c.  c.  of  serum  j)lus  (lisea>c-|)ro(iucing  blood,  I  with  lOc.  c. 
of  serinn  alone,  I  with  20  c.  c.  of  scrum  alone,  and  2  with  2  c.  c.  of 
di.sease-producing  blood  aloni".  Two  pen  checks  were  placed  with 
each  lot  of  serun)-sinuiltane<»us  trcatc«l  hogs  and  one  with  the  hogs 
injj'cted  with  disease-producing  blood  alone.  Table  21  shows  that  } 
of  the  (i  hogs  treated  with  10  c.  c.  of  serum  |)lus  di.sejise-producing 
1284()— .\o.  lO-J— OS h 


66 


PRODUCTION    OF   IMMUNITY   FROM    HOG   CHOLERA. 


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TESTS    OF    SERUM    FROM    SYPHAX    IMMUNES.  67 

blood  died  from  the  treatment,  but.  strange  to  say,  the  checks  in  the 
same  pen  did  not  contract  the  disease  from  them;  the  hogs  that 
received  20  c.  c.  of  serum  wath  disease-producing  blood  all  remained 
well,  as  did  those  injected  A\'ith  serum  alone.  The  2  hogs  injected 
with  disease-producing  blood  alone  died  of  hog  cholera,  as  did  the 
check  exposed  in  the  pen  with  them. 

The  surviving  hogs  from  the  protective  inoculations,  including  4 
pen  checks  (1902,  1903,  1910,  and  1911)  which  had  not  been  sick, 
were  exposed  to  hog  cholera  at  different  lengths  of  time  after  vaccina- 
tion. 

Of  the  hogs  treated  with  serum  alone,  2  that  received  10  c.  c.  and  2 
that  received  20  c.  c.  of  serum  were  placed  in  the  Scribner  exposure 
pen  eighteen  days  after  vaccination  with  2  of  the  pen  checks;  both  of 
the  checks  and  3  of  the  4  serum-treated  jiigs  died  of  hog  cholera.  The 
surviving  treated  hog  was  one  that  had  received  20  c.  c.  of  serum. 
The  4  remaining  hogs  treated  with  serum  alone  were  exposed  first 
sixty-eight  days  after  vaccination,  and  3  out  of  4  died  of  iiog  cholera, 
the  surviving  hog  being  again  one  of  those  that  received  20  c.  c.  of 
serum,  though  it  is  very  doubtful  whether  the  resistance  of  this  hog 
can  be  properly  attributed  to  the  previous  serum  injection.  The 
behavior  of  the  serum-simultaneous  hogs  after  exposure  to  hog  chol- 
era was  quite  different  from  that  of  the  hogs  treated  with  serum  aloiie. 

It  will  be  remembered  that  12  hogs  were  vaccinated  by  the  serum- 
simultaneous  method,  and  of  these  4  died  as  a  result  of  vaccination, 
these  having  received  only  10  c.  c.  of  serum  with  the  disease-producing 
blood.  The  2  surviving  hogs  that  received  10  c.  c.  of  scrum  plus 
disease-producing  blood  were  placed  in  the  vScribner  exposure  pen 
with  3  of  those  treated  with  20  c.  c.  of  serum  plus  diseaso-j^rothicitig 
blood  thirty-four  davs  after  vacchiation;  all  of  these  hogs  reuuii  .ed 
well,  although  the  2  checks  (1902  and  1903)  exposed  at  the  same 
time  died  of  hog  cholera.  The  3  remaining  hogs  treated  with  20  c.  c. 
of  senim  plus  <iisea,se-j)ro(hicing  l)Ioo<l  \v(>re  first  exj)ose<l  to  hog 
cholera  l)V  being  placed  in  the  Sc'ribner  exposure  jxmi  seventy-two 
days  after  vaccination.  All  of  them  renuu  'ed  well,  ahhougli  UTivac- 
cinated  check  hogs  2()()3.  2004,  and  200"),  subjected  to  the  same 
exposure  (bed  of  hog  cholera. 

Sintunnnj  of  t.i  furinifntK  trilli  first  ilriurin<i  <i(  si  nun  Jntiii  iinnnnu  l-iio. 

Results  of  rucci nation.  Kiglitecu  hogs  were  vaccinated  l)y  the 
serum-simultaneous  method;  of  these  10  rec<'ive(l  10  c.  c.  or  less  of 
serum,  while  the  remaining  s  received  !."»  c.  c.  (»r  more  <»f  serum. 
Eight  out  of  the  lirst  10  became  sick,  and  <»  iVin],  ns  a  result  of  vacci- 
nation, while  none  of  the  S  hogs  (hat  receiveil  liirger  doses  of  serum 
became  sick.  Four  hogs  that  were  injected  with  di^cjise-producing 
blood  alone  died  of  hog  cholera  as  a  result  of  the  injection.  The  S 
hogs  that  were  injected  with   serum   alone  as  usual   renuiined  well. 


68  PRODUCTION    OF    IMMUNITY    FROM    HOG    CHOLERA. 

All  pen  checks  with  vaccinated  hogs  remained  well,  notwithstanding 
the  fact  that  some  were  exposed  to  hogs  that  died  as  a  result  of 
vaccination. 

Results  of  exposure  to  hog  cholera. — Twelve  hogs  treated  by  the 
serum-simultaneous  method  were  exposed  to  hog  cholera  after 
vaccination,  some  being  exposed  after  an  interval  of  twenty-four 
days  while  others  were  not  exposed  until  approximately  two  and 
one-half  months  after  vaccination.  Of  these  hogs  only  2  had  shown 
symptoms  of  sickness  after  vaccination.  None  of  the  12  became 
sick  as  a  result  of  exposure.  Eight  hogs  that  had  been  treated  with 
serum  alone  were  exposed  to  hog  cholera,  4  being  exposed  eighteen 
days  after  vaccination,  and  4  two  months  and  eighteen  days  after 
vaccination;  6  of  these  died  of  hog  cholera.  Five  unvaccinated  hogs 
were  exposed  with  the  treated  hogs  as  checks,  and  all  of  these  died 
of  hog  cholera. 

From  these  experiments  we  may  conclude  that — 

(1)  The  serum  from  hog  1310,  first  drawing,  ^vill,  when  given  in 
sufficient  dose,  protect  hogs  from  a  fatal  dose  of  disease-producing 
blood  administered  simultaneously  with  the  serum. 

(2)  This  simultaneous  vaccination  confers  on  the  treated  hogs  an 
immunity  which  lasts  for  at  least  two  and  one-half  months. 

(3)  The  immunity  in  hogs  which  showed  no  symptoms  after  vac- 
cination seems  to  be  quite  as  firm  as  in  those  that  were  made  visibly  ill. 

(4)  Serum  alone  did  not  confer  a  satisfactory  immunity  for  even 
three  weeks  in  the  dose  used. 

(5)  The  immunity  in  serum-simultaneous  hogs  was  not  due  to  the 
action  of  the  serum  alone. 

(6)  Check  hogs  exposed  to  hogs  which  became  sick  as  a  result  of 
vaccination  contracted  disease  from  them  in  some  cases. 

PRODUCTION  OF  A  PROTECTIVE  SERUM   BY  USING  A   REDUCED  DOSE  OF 

DISEASED    BLOOD. 

The  hogs  in  the  preceding  experiments  that  were  hypeiimmunized 

by  the  "quick   method"    all  received  a   dose  of  disease-producing 

blood  in  the  proportion  of  1,000  c.  c.  of  blood  to  100  pounds  of  body. 

We  have  carried  out  only  one  experiment  with  serum  from  an  immune 

hyperimmunized  with  a  smaller  dose  of  disease-producing  blood. 

This  hog  (1401)  received  only  500  c.  c.  of  disease-producing  blood 

for  hyperimmunization.     The  history  of  hog  1401,  as  well  as  the 

experiments  carried  out  wdth  serum  from  that  hog,  are  described 

below. 

Experiment  XIX. — Serum  from  imviune  14OI. 

Hog  1401  is  one  of  those  that  was  vaccinated  by  the  serum-simul- 
taneous method  in  the  experiments  of  1905,  and  its  detailed  history 
is  as  follows: 

Hog  1401  weighed  60  pounds  December  2,  1905,  and  on  this  date, 
together  with  other  hogs,  was  injected  simultaneously  with  disease- 


EXPERIMENTS   WITH   A  REDUCED  DOSE  OF   DISEASED  BLOOD.       69 

producing  blood  and  10  c.  c.  of  serum  from  immune  1234  (see  p.  11). 
No  symptoms  of  sickness  followed  tliis  injection,  and  the  hog  was 
exposed  to  disease  on  December  27,  1905.  Hog  1401  again  remained 
well  and  was  not  further  exposed  until  September  3,  1906,  when  it 
was  injefcted  subcutaneously  \viih  500  c.  c.  of  Scribner  disease-pro- 
ducing blood.  The  weight  of  the  hog  at  this  time  was  approximately 
100  pounds.  No  visible  disturbance  of  health  followed  tliis  injection. 
On  September  24,  1906,  just  three  weeks  after  the  injection  of  dis- 
ease-producing blood,  hog  1401  was  bled  in  order  to  secure  serum 
for  experimental  purposes.  This  hog  may  be  classed  with  the  Scrib- 
ner (juick  immunes,  though  the  dose  of  serum  used  in  proportion  to 
the  body  weight  of  the  immune  is  only  half  of  that  used  on  the  other 
Scribner  quick  immunes. 

Unfortunately,  we  were  not  able  to  carry  out  as  extensive  experi- 
ments with  this  serum  as  was  desirable,  but  the  number  of  animals 
available  for  experimental  purposes  and  the  retpiirements  of  other 
experiments  in  the  way  of  pens  and  hogs  made  it  impossible  to  do 
more  than  make  a  preliminary  test  of  the  potency  of  the  serum  from 
inunune  1401. 

The  tests  of  this  serum  were  made  in  the  usuai  manner,  the  serum 
being  used  in  doses  of  5c. c,  10  c.  c,  and  15  c.  c,  given  simultaneoush' 
with  a  fatal  dose  of  disease-producing  blood.  Table  22  shows  the 
results  of  these  injections.  Both  of  the  hogs  injected  with  only  5  c.  c. 
of  serum  became  sick  and  1  died,  and  they  also  communicated  disease 
to  their  pen  check,  hog  1814.  One  of  the  2  hogs  that  were  injected 
with  lOc.c.  of  serum  ])lus  disease-producing  lilood  became  slightly 
sick  but  recovered,  wliile  the  other  remained  well;  tiie  pen  check  in 
this  pen  contracted  hog  cholera.  Neither  of  the  hogs  that  received 
15  c.  c.  of  senim  with  the  disease-producing  blood  showed  any  symp- 
toms of  illness  following  vaccination,  and  their  pen  check  likewise 
remained  well.  Both  of  the  hogs  that  were  injected  with  disease- 
producing  l>lood  alone  died  of  hog  cholera  and  connnunicated  the 
disease  to  their  pen  check,  hog  1S23. 

It  will  thus  be  seen  that  of  6  i»ogs  inoculated  simultaneously  with 
serum  and  diseased  ])l<)od,  3  became  sick  but  only  1  died,  and  this  one 
received  the  smallest  dose  (5  c.  c.)  of  senim.  Four  of  the  5  surviving 
vaccinated  hogs  were  later  exposed  to  hog  cholera  to  test  the  duration  of 
the  immunity  conferred  by  vacciiuition.  Two  of  these  hogs  were  placed 
in  the  Scribner  exposure  pen  on  November  17,  190(),  thirty  days  after 
vaccination:  thestirviving])en  check. hog  1S20.  was  exposed  at  thesamc 
time.  The  check  died,  but  both  of  the  treated  hogs  remained  well. 
The  2  other  vaccinated  hogs  were  first  exposed  to  hog  cholera  three  and 
one-half  months  after  vaccination.  They  both  remained  well,  although 
unprotected  hogs  exposed  at  the  same  time  died  of  hog  cholera. 

Although  we  have  hyjierim  muni  zed  ojdy  1  hog  by  the  (piick 
method  with  a  dose  of  disease-producing  blood  e(jual  to  500  c.  c.  ]ier 
100  pounds  of  body  weight,  tiie  results  obtaini'd  with  this  serum  are 


70 


PRODUCTION    OF   IMMUNITY   FROM    HOG   CHOLERA. 


such  that  there  is  good 
reason  to  believe  that 
this  reduced  dose  might 
be  sufficient  to  produce 
a  satisfactory  serum. 
Owing  to  reasons  al- 
ready stated,  we  have 
not  as  yet  been  able  to 
decide  this  point,  but 
fi'om  what  has  been 
done  we  may  conclude 
that  (1)  the  serum  of 
hog  1401  is  as  potent 
as  that  of  some  other 
immunes  injected  with 
larger  doses  of  disease- 
producing  blood,  but 
that  it  is  not  equal  in 
potency  to  that  from 
the  majority  of  immunes 
which  received  twice  as 
much  disease-producing 
blood;  (2)  when  given 
in  sufficient  dose  this 
serum  will  protect  pej'- 
f ectly  from  a  fatal  dose  of 
disease-producing  blood 
administered  sinuiltane- 
ously  with  theserum ;  (3) 
the  immunity  produced 
by  the  senim-simultane- 
ous  injections  lasted  at 
least  three  and  one-half 
months,  even  though 
the  treated  hogs  showed 
no  signs  of  reaction  af- 
ter injection;  (4)  it  ap-, 
pears  possible  that  the 
injection  of  serum  did 
not  lower  the  infectious- 
ness of  the  disease  to 
as  great  an  extent  as 
other  sera  from  immimes 
that  were  given  larger 
doses  of  diseased  blood, 


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SEBUM   FROM    NONHYPERIMMUNIZED   IMMUNES.  71 

for  pen  check  1817  contracted  hog  cholera  from  exposure  to  hogs 
1815  and  1816,  although  only  one  of  these  became  slightly  sick. 
It  will  be  remembered  that  as  a  rule  the  pen  checks  with  serum- 
simultaneous  vaccinated  hogs  remained  well,  and  that  when  the  vac- 
cinated hogs  were  made  desperately  sick  by  the  treatment  the  pen 
checks  occasionally  contracted  disease. 

EXPERIMEXTS    WITH    SERUM    FROM    NONHYPERIMMUNIZED   IMMUNES. 

In  view  of  the  very  marked  protective  power  possessed  by  the 
serum  of  hog  1401,  as  shown  in  the  experiment  just  described,  it  was 
considered  advisable  to  test  the  serum  from  at  least  2  immunes  that 
had  not  been  given  any  injections  of  diseased  blood  for  the  purpose 
of  hyperimmunization.  Previous  experiments  of  this  character  had 
not  revealed  any  noticeable  protective  power  in  the  blood  of  normal 
immunes,  but  nevertheless  for  the  sake  of  comparison  it  was  deemed 
best  to  repeat  those  tests.  The  history  of  the  2  immimes  selected 
for  this  work  is  given  in  brief  in  connection  with  the  tests  of  serum 
from  each  of  them  described  below. 

ExPEKiMENT  XX. — Serum  from  nnnhyperimmunized  hnmiirw  1-'i-^'i- 

This  hog  was  vaccinated  by  the  serum-simultaneous  method  in  the 
1905  experiments,  as  noted  in  Table  3  of  this  paper.  The  detailed 
history  is  as  follows:  On  December  16,  1905,  hog  1424,  which  weighed 
at  that  time  45  pounds,  was  injected  simultaneously  ^nth  2  c.  c.  of 
disease-produc'ng  blood  and  10  c.  c.  of  hy]:)erimmune  serum  from  hog 
12.34,  No  visible  symptoms  of  illness  followed  this  injection,  although 
the  sanie  diseased  blood  caused  the  death  of  all  unprotected  hogs 
that  were  injected  at  the  same  time.  (See  Table  3.)  On  January  9, 
1906,  this  hog  wa.s  exposed  to  virulent  disease  by  being  placed  in  the 
exposure  pen.     This  exposure  was  without  effect. 

On  October  8,  1906,  blood  was  drawn  from  hog  1424,  and  after 
being  defibrinated  and  mixed  with  the  carbolic  acid  solution  in  the 
u.sual  manner  it  was  used  in  the  following  experiment. 

Two  hogs  were  injected  with  10  c.  c.  each  of  serum  from  hog  1424 
plus  disease-producing  blood,  and  2  with  20  c.  c.  each  of  senim  plus 
disea.se-producing  blood.  One  untreate<l  healthy  hog  was  ])laced 
in  the  pen  with  each  lot  in  the  usual  manner,  and  2  hogs  were  inocu- 
lated with  disease-producing  blood  alone,  a  check  l)eing  placed  in  the 
pen  with  these  also.  The  maimer  of  carrying  out  this  experiment 
and  the  results  obtained  arc  very  well  shown  in  Tabl<'  23. 

From  Table  23  it  may  be  seen  that  the  4  hogs  that  were  injected 
with  (lis(Mise-pro(lucing  blood  and  scrum  Ix'came  sick.  It  will  be 
seen,  however,  that  only  2  of  these  (lic(|.  while  both  of  those  that 
received  disease-producing  blood  alone  died.  It  may  also  be  of  sig- 
nificance, though  not  necessarily  so,  thai  l)oth  of  llic  vaccinated  hogs 
that  died  showed  symj)toms  of  disease  .somewhat  later  than  the  hogs 


72 


PRODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 


that  received  no  senim,  and  tliey 
also  lived  a  longer  time.  From 
the  small  number  of  tests  carried 
out  it  can  not  be  stated  with 
complete  assurance  that  this 
greater  resisting  power  on  the 
part  of  the  vaccinated  hogs  was 
due  to  the  influence  of  the  im- 
mune serum. 

Experiments  with  Serum  from  Non- 

-HYPERIMMUNIZED    ImMUNE    1295. 

In  order  to  test  further  the 
value  of  nonhyi^erimmunized 
immune  serum,  the  blood  of 
another  immune  was  used  in  the 
follow^ing-described  experiment : 

Immune  hog  1295  was  selected 
for  comparison  with  hog  1424  be- 
cause the  latter  had  never  shown 
any  symptoms  of  illness  after  ex- 
posure to  hog  cholera,  while  the 
former  had  recovered  from  a  mild 
attack  of  that  disease.  It  might 
be  supposed,  therefore,  that  hog 
1424  possessed  natural  immu- 
nity, while  hog  1295  probably 
acquired  immunity  through  a 
mild  attack  of  hog  cholera.  This 
supposition  in  regard  to  hog  1424 
is  not  of  necessity  true,  however, 
because  our  experiments  have 
shown  that  susceptible  hogs 
rarely  become  sick  after  vaccina- 
tion, and  it  is  quite  probable 
that  hog  1424  acquired  immun- 
ity from  vaccination.  This  hog 
1295  was  first  exposed  to  hog 
cholera  on  September  12,  1905. 
At  that  time  the  hog  weighed 
100  pounds.  The  exposure  to 
disease  was  made  by  the  subcu- 
taneous injection  of  disease- 
producing  blood.  Following 
this  injection  hog  1295  became 


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SEEUM   FROM    NONHYPERIMMUNIZED   IMMUNES. 


73 


distinctly  though  not  desperately  sick,  sho\ving  the  usual  symptoms 
of  a  rather  mild  attack  of  hog  cholera.  After  recovery  from  this  illness 
hog  1295  was  placed  in  the  exposure  pen,  but  did  not  become  sick. 
This  hog  was  finally  removed  from  the  exposure  pen,  but  was  not 
again  exposed  to  hog  cholera.  Blood  was  d^a^vn  from  hog  1295  on 
November- 22,  1906,  and  after  being  prepared  in  the  usual  manner 
was  used  in  the  experiment  next  described. 

Experiment  XXI. — Serum  from  nonhyperimvinnized  immune  1295. 

This  experiment  was  modeled  directly  after  the  preliminary  experi- 
ments with  the  hyperimmune  serum,  the  serum-simultaneous  method 
only  being  used,  as  previous  experiments  had  shown  that  all  of  the 
hyperimmunized  hogs  furnished  serum  that  would  protect,  when 
given  in  sufficient  dose,  from  a  simultaneous  injection  of  disease- 
producing-blood,  and  it  was  evident  that  a  failure  to  protect  from  a 
simultaneous  injection  of  such  blood  would  certainly  render  unneces- 
sary an  experiment  to  determine  the  duration  of  immunity  conferred 
by  serum  alone. 

T.\BLE  24. — Experiment  rrith  srriimfmm  hnr/  12!>')  tnnnhyprrimm}ini:efl  immune). 


No.  ol 
hog. 


Inoculation. 


Weight. 


Matprial  injci'teii. 


Diito. 


1920. 

1921. 
1922. 
1923. 

1924. 
1925. 

1920. 

1927. 

1928. 

1929. 

19.-J0. 

1931. 


Pound  g. 
45 


5  c.  c.  serum  and  2  p.c.  (lis-  \  Nov.  Zi,  liKHl 

ease-producing    blood    vl 

hog  1891. 
do do 


Pen  chock   with  hojis   I'.t2()    

and  1921. 
10  c.c.  scrum  and  2  c.c.  dis-  j  Nov.  Zi,  HKXi 

eas<>-i)roducing    blood    (t 

hog  1891. 

....  do do 

Pen  check   with   hogs   KtZJ    

and  1924. 
l.'i  c.  c.  sjTUm  and  2  c.  c.  di.H-      Nov.  2.S,  KKXi 

ea8«'<l  blood  of  hog  isill . 
do <lo 


Pen   check   with  hogs    192tl    

and  1927.  i 

2    c.    c.    disi'a.se-prodncing      Nov. 

bloo<iolhog  1N91. 
do <l< 


I'en  che<'k   with   hogs   lifJit 
and  19;«). 


Ucsult. 


Sick    Nov.    2<);    died 
Dec.  1,1906. 

Sick     Nov.     29:  died 

Dec.  2.  190(). 
Sick      Dec.      S;  died 

Dec.  l(i,  U*Oi'>. 
Sick    Nov.    2^»;    dieii 

Dec.  2,  liKXi. 

SickNov.29. 190f.:died 
Sick    Dec.    l.i;  killed 

Dec.  20.  190ti. 
Sick    Nov.    2".t;     <lied 

Dw.  1.  I'.tOti. 
Sick    Nov.    2'.i;    died 

De<-.  .■?,  190t). 
Sick     D<v.     .1;     die<l 

l)t>c.9.  lIKXi. 
Sick     Nov.    29;    died 

D(v.  2.  liKX.. 
Sick    Nov.    2".»;    died 

Dec.  3,  llKXi. 
Sick     Dw.     K:      ilie<l 

Dec.  19,  190»i. 


-Xntopsy. 


Hemorrhagic 

lesions. 

Do. 

Hemorrhages 
and  ulcers. 

Hemorrhagic 
lesions. 

Do. 
No  markeil  le- 
sions. 
Hemorrhagic 
lesions. 
Do. 

Hemorrhages 
and  ulcers. 

Hemorrhagic 
lesions. 

Hemorrha  ges 
and  ulciTS. 
Do. 


Table  24  shows  without  question  tlw  lack  of  potency  of  tlic  scnini 
from  hog  1295.  Doses  of  15  c.  c.  of  serum  (hd  not  prove  to  !)<>  any 
more  potent  than  doses  of  5  <•.  c..  and  every  liog  in  (his  (vxperiincnt 
died  of  hog  cholera,    the   di.sca.sc    Ix-ing  comniunicatcd   to   the   jx'n 


74  PRODUCTION   OP   IMMUNITY  FROM   HOG  CHOLERA. 

checks  in  all  cases.  It  does  not  appear  that  the  serum,  even  in  the 
largest  doses,  exercised  any  retarding  influence  upon  the  incubation 
period  or  upon  the  course  of  the  disease  once  it  had  appeared. 

Summary  of  results  obtained  with  serum  from  nonhyperimmunized  im,m,unes. 

Serum  from  2  immunes  was  used  in  doses  of  from  5  c.  c.  to  20  c.  c, 
and  this  serum  was  injected  into  nonimmunes  simultaneously  with 
a  fatal  dose  of  disease-producing  blood.  Ten  were  treated  by  this 
process;  all  contracted  hog  cholera,  and  8  died  of  that  disease.  Of 
4  hogs  injected  with  disease-producing  blood  alone,  all  died  of  hog 
cholera.  Five  checks  were  placed  in  the  pens  with  the  vaccinated 
hogs,  and  all  contracted  disease  from  them  and  died.  The  2  pen 
checks  exposed  in  the  pen  with  the  hogs  that  received  disease- 
producing  blood  only  also  died'  of  hog  cholera. 

From  the  results  stated  above  it  will  be  seen  that  (1)  the  protec- 
tion afforded  to  nonimmune  hogs  by  the  injection  of  serum  from 
nonhyperimmunized  immunes  is  very  slight  as  compared  with  that 
afk)rded  by  hyperimmune  serum;  (2)  even  in  doses  of  20  c.  c.  the 
protection  afforded  was  not  sufficient  to  prevent  the  death  of  1  of 
the  2  animals  that  received  that  dose;  (3)  the  contagiousness  of 
the  disease  is  not  noticeably  lessened  by  the  injection  of  serum 
from  a  nonhyperimmunized  immune;  and  (4)  the  serum  from  non- 
hyperimmunized immunes  is  not  potent  enough  to  render  its  use 
practicable  in  combating  hog  cholera. 

EXPERIMENTS    WITH    SUCKLING    PIGS. 

The  following  experiments  with  young  pigs  were  carried  out  for 
the  purpose  of  determining  whether  very  young  pigs  would  react 
to  vaccination  with  immune  serum  in  the  same  manner  as  the  larger 
shoats.  It  was  desirable  to  determine  also  whether  very  much 
smaller  doses  of  serum  might  not  be  used  on  the  small  pigs,  thus 
effecting  a  considerable  saving  in  the  cost  of  vaccination.  The 
plan  adopted  was  to  vaccinate  part  of  a  litter  of  pigs  and  leave  part 
unvaccinated,  so  that  when  the  time  came  for  testing  the  immunity 
of  the  vaccinated  pigs  we  would  have  a  sufficient  number  of  checks 
for  exposure  along  \dth  the  vaccinated  pigs,  and  additional  infor- 
mation regarding  the  danger  of  hog  cholera  being  transmitted  tlu"ough 
the  agency  of  vaccinated  hogs  would  also  be  secured. 


EXPERIMENTS    WITH    SUCKLING   PIGS. 


75 


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Experiment  XXII . — Serum-simul  taneous 
vaccination  of  suckling  pigs,  using  serum 
from  immune  1383. 

The  5  suckling  pigs  used  in  this  ex- 
periment were  10  days  old  at  the  time 
of  vaccination  and  all  were  vigorous 
and  healthy.  Two  older  pigs  (1730 
and  1731)  were  injected  at  the  same 
time  as  the  suckling  pigs  with  disease- 
producing  blood  alone,  in  order  to  test 
the  virulence  of  the  blood.  By  re- 
ferring to  Table  25  the  method  of  car- 
rying out  the  experiment  may  be  best 
understood. 

Three  of  the  suckling  pigs  were 
given  2  c.  c.  each  of  serum  wdth  0.25 
c.  c.  of  disease-producing  blood  sul)- 
cutaneously;  the  remaining  2  were 
not, treated,  but  the  entire  litter  was 
left  together,  the  sow  being  given  40 
c.  c.  of  serum  as  a  protection  against 
possible  infection  from  the  vaccinated 
pigs.  No  pigs  were  injected  A\-ith  0.25 
c.  c.  of  disease-producing  blood  alone, 
but  the  death  of  pig  1726  and  the  sick- 
ness of  1725,  in  spite  of  the  injection 
of  the  serum,  indicate  that  0.25  c.  c. 
of  the  disease-producing  blood  used 
in  this  experiment  would  prt)bably 
have  been  suHicient  to  destroy  all  of 
the  injected  pigs  if  the  seriun  had  not 
been  used.  The  virulence  of  the 
disease-producing  blood  in  tlu»  usual 
dose,  2  c.  c,  is  shown  by  the  records 
of  hogs  1730  and  1731,  and  the  con- 
tagiou.sness  of  the  disease  is  proven 
by  the  sickness  and  death  of  uninoc- 
ulateil  hog  1732,  exposed  in  the  i)en 
with  hogs  1730  and  1731.  These  :> 
hogs — 1730,  1731,  and  1732 — were  of 
course  placetl  in  a  |)en  to  tiiemselv«'s 
and  did  not  at  any  time  associate 
with  the  other  hogs  in  this  exix'ri- 
ment.  Tbe  low  degree  of  contagious- 
ness of  the  (liseasr  following  vaccina- 


76  PRODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 

tion,  which  has  been  remarked  upon  in  connection  with  other  experi- 
ments already  descri))ed,  is  a<?ain  well  shown  in  this  experiment, 
where  the  uninoculated  sucklinjj;  pigs  remained  well  even  though 
the3"  associated  with  pig  1726,  which  died  from  vaccination. 

The  4  surviving  pigs — 1725,  1727,  1728,  and  1729 — were  with  the 
mother  transferred  to  a  pasture  that  was  free  from  hog  cholera.  All 
remained  well,  and  approximately  four  months  after  vaccination 
they  were  weaned.  Shortly  after  this,  pigs  1725  and  1728  became 
sick  and  died.  Neither  showed  lesions  of  hog  cholera,  and  as  there 
is  nothing  to  show  that  disease  had  ever  been  introduced  into  this 
pasture,  we  must  consider  the  death  of  these  pigs  to  have  been  due 
to  some  other  cause,  the  exact  nature  of  which  we  were  not  able  to 
determine.  For  this  reason  Table  25  does  not  show  the  history  of 
pigs  1725  and  1728  subsequent  to  vaccination.  The  remaining  pigs 
of  this  litter,  1727  and  1729,  one  a  vaccinated  pig  and  the  other  a 
check,  were  placed  in  the  Scribner  exposure  pen  on  February  20, 1907, 
just  five  months  after  pig  1727  had  been  vaccinated.  As  a  result  of 
this  exposure  the  check  (1729)  sickened  and  died  on  March  10,  1907, 
while  the  treated  pig  (1727)  remained  well.  The  results  of  this 
exposure  furnish  adtlitional  proof  that  the  death  of  pigs  1725  and 
1728  in  the  pasture  before  exposure  was  not  due  to  hog  cholera,  for, 
upon  undoubted  exposure  to  that  disease,  vaccinated  pig  1727, 
treated  in  the  same  manner  as  pig  1725,  remained  well,  while  the 
check  (1729)  died,  thus  indicating  that  had  the  disease  in  the  pasture 
been  hog  cholera  the  vaccinated  pig  (1725)  would  not  have  suc- 
cumbed, while  pig  1729,  which  was  later  found  to  be  susceptible, 
would  have  contracted  disease  at  that  time. 

Owing  to  the  loss  of  1  of  the  pigs  of  this  litter  from  vaccination  and 
of  2  others  through  an  intercurrent  disease,  as  just  explained,  this 
experiment  does  not  throw  very  much  light  upon  the  feasibility  of 
vaccinating  suckling  pigs.  It  does  indicate,  however,  that  the  serum 
of  hog  1383,  in  doses  of  2  c.  c,  is  sufficient  in  most  cases  to  protect 
pigs  weighing  5  pounds  from  a  fatal  dose  of  disease-producing  blood 
administered  simultaneously  with  the  serum.  It  appears  also  that 
the  serum  exerted  decided  influence  in  lessening  the  contagiousness  of 
the  disease.  The  weight  that  should  be  attached  to  the  death  of 
check  pig  1729  and  the  survival  of  vaccinated  pig  1727  when  exposed 
together  to  hog  cholera  can  only  be  properly  considered  in  connection 
with  the  behavior  of  other  pigs  under  similar  conditions  and  treated  in 
a  similar  manner. 


EXPERIMENTS    WITH    SUCKLING    PIGS. 


77 


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Experiment  XXIII. — Serum-simul- 
taiuotis  vaccination  of  suchliiig  pigs, 
using  serum  from  immune.  1313.  « 

Seven  suckling  pigs,  all  of 
the  same  litter  and  about  2 
weeks  old,  were  used  in  this 
experiment.  The  weight  of 
these  pigs  was  approximately 
9  pounds  each,  with  the  ex- 
ception of  2  of  those  reserved 
as  checks,  which  were  a  very 
little  lighterin  weight.  Of  the 
vaccinated  pigs,  2  were  given 
3  c.  c.  of  serum  from  hog  1318 
and  2  were  given  4  c.  c.  of 
the  same  senim,  each  receiv- 
ing at  the  same  time  0.25  c.  c. 
of  Scribner  disease-producing 
blood.  The  remaining  3  ])igs 
were  left  imtreated  to  serve 
as  controls,  l^nfortunately, 
as  in  Experiment  XXII,  we 
did  not  have  a  sufficient  num- 
ber of  pigs  to  permit  the  in- 
jection of  some  with  0.2o  c.  c. 
of  disease  -  pro(hicing  blood 
alone  and  thus  determine  the 
protection  afforded  by  the  se- 
rum at  the  time  of  vaccina- 
tion. For  tliis  reason  we  were 
forced  to  be  content  with  the 
injection  of  larger  pigs  witli  a 
larger  do.se,  2  c.  c.  of  diseas(>- 
])roducing  blood.  The  vacci- 
nated and  the  unvacciiiated 
j)igs  of  tliis  litter  were  left  to- 
gether with  tlie  sow  aft<M-  the 
vaccination:  the  larger  |>igs, 
1S21  and  1S22,  that  were  in- 
j(>ct('d  witli  disease-producing 
1 )  1( )( »d  ( )n  ly , a nd  t  heir  pen  check. 
1S2.3,  were  |)la<'<'<l  in  a  jxMi  to 
them.selves. 


VV    5V'    V'/iy^v!    "J.    "i 


«'  Fiirliisliiry  nf  this  immuiic  scip.  IM  . 


78  PRODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 

The  death  of  the  2  hogs  (1821  and  1822)  from  the  diseased  blood 
injection  and  the  sickness  and  death  of  hogj  1823  from  association 
with  these  two  show  the  virulence  and  the  contagiousness  of  the  dis- 
ease produced  by  the  blood  used  in  the  vaccination  of  the  suckling  pigs. 
.  All  of  the  vaccinated  suckling  pigs  became  slightly  sick  about 
twelve  days  after  vaccination.  The  symptoms  exhibited  were 
droopiness  and  conjunctivitis,  and  slight  diarrhea  in  some  cases;  this 
had  all  passed  away  after  four  or  five  days.  None  of  the  untreated 
pigs  became  sick.  After  the  recovery  of  the  vaccinated  pigs  the  entire 
litter  with  the  mother  was  placed  in  a  pasture  free  from  disease.  They 
all  thrived,  and  after  being  weaned  were  placed  in  the  Scribner  exposure 
pen  on  February  20,  1907,  approximately  four  months  after  vaccina- 
tion. As  a  result  of  this  exposure  all  of  the  checks  died  and  showed 
at  autopsy  the  typical  lesions  of  hog  cholera.  In  marked  contrast  is 
the  behavior  of  the  vaccinated  pigs,  none  of  which  became  sick  in  the 
exposure  pen. 

The  results  of  tliis  experiment  indicate  (1)  that  suckling  pigs  may 
be  vaccinated  by  using  smaller  doses  of  serum  and  disease-producing 
blood  than  is  feasible  in  the  case  of  larger  hogs;  (2)  that  the  immunity 
conferred  by  the  injection  of  these  small  doses  of  serum  and  disease- 
producing  blood  is  quite  durable,  and  (3)  that  the  A^accinated  pigs  are 
not  likely  to  transmit  hog  cholera  to  unprotected  pigs  that  associate 
with  them. 

ExPEUiMENT  XXIV. — Serum-simultaneous  vaccination  of  suckling  pigs,  using  serum 

from  immune  121  A- 

The  pigs  used  in  this  experiment  were  10  days  old  and  weighed 
about  6  pounds  each.  On  November  1,  1906,  3  of  them  were  injected 
simultaneously  with  3  c.  c.  of  serum  and  0.25  c.  c.  of  disease-producing 
blood  and  3  were  left  untreated.  Two  larger  hogs  (1867  and  1868) 
were  given  2  c.  c.  of  diseased  blood  alone,  and  an  untreated  hog 
was  placed  in  the  pen  as  a  control  on  the  contagiousness  of  the  disease. 
Table  27  shows  very  clearly  that  this  experiment  was  not  a  success, 
for  2  of  the  3  vaccinated  pigs  died  as  a  result  of  the  treatment  they 
received  and  1  of  the  checks  contracted  disease  from  these  and  died, 
thus  leaving  only  1  treated  pig  with  2  checks  for  subsequent  exposure. 
This  exposure,  which  took  place  three  months  and  twenty  days  after 
vaccination,  caused  the  death  of  1  of  the  checks,  while  the  2  other  pigs 
remained  well.  Incidentally  these  results  show  that  0.25  c.  c.  of  the 
disease-producing  blood  used  in  this  experiment  was  sufficient  to 
cause  the  death  of  suckling  pigs. 


EXPERIMENTS   WITH   SUCKLING   PIGS. 


79 


Experiment  XXV. — Immunization  of 
suckling  pigs  with  serum  alone  from 
immune  1274. 

This  experiment  was  designed 
to  determine  the  protective 
power  of  the  serum  when  used 
alone.  A  litter  of  9  healthy 
pigs,  1  week  old  and  weighing 
about  6  pounds  each,  was  used. 
Five  of  these  pigs  were  given 
5  c.  c.  each  of  serum  from  hog 
1274  subcutaneouslyon  Novem- 
ber 14,  1906,  and  the  remaining 
4  pigs  were  left  untreated.  As 
was  to  be  expected,  no  sickness 
followed  the  injection  of  the 
serum,  and  the  mother,  with 
the  entire  litter  of  pigs,  was 
placed  in  a  lot  supposed  to  be 
free  from  disease.  They  all 
remained  well  until  some  time 
tluring  the  month  of  January", 
when  the  checks  were  found  to 
be  sick.  Pig  1988  was  the  first 
of  these  to  die,  but  the  other  3 
checks  did  not  live  much  longer. 
The  vaccinated  pigs  all  remained 
well.  From  the  lesions  found 
at  the  autopsy  on  the  checks 
there  seems  to  be  no  reason  to 
doubt  that  these  pigs  died  of 
hog  cholera.  We  are  unable  to 
determine  just  when  they  were 
first  exposed  to  infection,  but 
it  seems  probable  that  this 
exiwsure  took  place  about  ten 
or  twelve  days  prior  to  the  death 
of  the  first  pigs.  This  would 
place  tlie  (hite  of  exposure  about 
January-  10,  approximately  two 
months  after  the  vaccination. 

It  Is  fair  to  a.ssume,  therefore, 
that  tlie  senim  alone  conferred 
uj)on  the  treated  pi<;s  immunity 
which  histed  for  two  months 
at  least. 


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PRODUCTION    OF   IMMUNITY   FEOM    HOG   CHOLERA. 


The  five  treated  pigs  were  given  another 
exposure  by  being  placed  in  the  Scrib- 
ner  exposure  pen  on  February  20,  1907. 
They  did  not  tlu'ive  in  this  pen,  but  none 
of  them  contracted  hog  cholera. 

Summary  of  results  with  suckling  pigs. 

In  looking  over  the  four  experiments 
which  have  just  been  described  and  wliich 
were  carried  out  with  very  young  pigs  it 
will  be  seen  that  serum  from  three  dif- 
ferent immimes  was  used,  and  this  was 
given  in  varying  doses.  For  tliis  reason 
it  is  not  possible  by  merely  averaging 
the  losses  among  vaccinated  and  un- 
vaccinated  pigs  to  determine  the  value 
of  the  serum  for  practical  use,  for  it  is 
probable  that  if  we  had  used  doses  of  5 
c.  c.  in  all  cases  there  would  have  been 
no  deaths  from  vaccination,  and  in  the 
light  of  the  experiments  with  older  pigs 
it  also  seems  probable  that  tliis  increased 
dose  of  serum  would  not  have  lessened 
the  duration  of  immunity  in  the  vacci- 
nated pigs. 

In  spite  of  the  facts  just  stated,  it  is  at 
least  interesting  to  consider  all  together 
the  results  of  the  experiments  with  suck- 
Ung  pigs.  With  3  of  the  litters  the  serum- 
simultaneous  method  was  used,  while 
serum  alone  was  used  for  vaccinating  the 
fourth  litter.  In  all,  10  suckling  pigs 
were  treated  by  the  serum-simultaneous 
method,  and  all  showed  more  or  less 
marked  symptoms  of  illness  after  vac- 
cination, 3  of  them  finally  dying  of  hog 
cholera.  The  remaining  7  recovered,  and 
6  of  these  were  exposed  to  hog  cholera 
in  an  infected  pen  from  three  and  one- 
half  to  five  montlis  after  vaccination; 
all  remained  well.  In  the  same  litters 
with  these  10  vaccinated  pigs  there  were 
8  untreated  pigs  reserved  as  checks. 
Only  1  of  these  checks,  all  of  which  asso- 
ciated \vith    the  vaccinated   pigs,  con- 


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CURATIVE    VALUE    OF    HYPERIMMUNE    SERUM.  81 

tracted  hog  cholera  from  them.  Of  the  7  remaining  checks,  6  were 
exposed  to  hog  cholera  along  with  the  6  vaccinated  pigs  described 
above.  Of  the  6  checks,  5  died  of  hog  cholera,  thus  showing  a 
marked  difference  from  the  6  vaccinated  pigs,  all  of  which  remained 
well. 

The  remaining  Utter  of  pigs,  it  will  be  remembered,  was  treated 
with  serum  alone,  5  being  given  5  c.  c.  of  senim  while  4  were  reserved 
as  checks  and  not  treated  in  any  way.  Of  these,  all  4  of  the  checks 
died  of  hog  cholera  when  exposed  two  months  later,  while  the  5  vac- 
cinated pigs  all  remained  well. 

The  experiments  with  suckling  pigs  are  not  sufficiently  extensive 
to  warrant  definite  conclusions  being  drawn,  and,  especially  in  view 
of  the  success  of  the  vaccination  with  serum  alone,  more  experiments 
designed  to  test  the  duration  of  immimit}^  resulting  from  such  injec- 
tions should  be  carried  out,  together  with  additional  experiments 
with  the  serum-simultaneous  method.  The  latter  ex])eriments 
should  be  carried  out  with  somewhat  larger  doses  of  senim,  and  the 
immunity  of  the  vaccinated  pigs  should  first  be  tested  at  the  end  of 
six  or  eight  months.  We  regard  such  experiments  as  being  of  great 
practical  importance  owing  to  the  lessened  cost  resulting  from  the 
reduced  dose  of  serum  and  the  longer  period  of  protection  that  might 
be  secured  by  vaccinating  suckling  pigs. 

CURATIVE  VALUE  OF  HYPERIMMUNE  SERUM. 

In  previous  pages  a  large  number  of  exj^eriments  dealing  with 
immunization,  through  the  use  of  senim  alone,  as  well  as  through  the 
combined  action  of  serum  and  disease-producing  blood,  have  been 
described,  but  in  those  experiments  no  attem])t  was  made  to  deter- 
mine the  curative  value  of  the  immune  serum. 

Two  experiments  wliich  wore  designed  to  tlu'ow  some  light  upon 
this  question  have  been  carried  out,  but  before  proceeding  to  a 
description  of  these  a  few  words  should  be  said  concerning  the  way  in 
which  the  hogs  used  in  these  experiments  were  exposed   to  infection. 

In  vaccinating  hogs  by  the  serum-sinmltaneous  method,  it  will  be 
remembered,  the  method  of  introducing  the  iiif(Htion  consisted  in  the 
injection  of  the  hogs  subcutaneously  with  a  fatal  dose  of  disease- 
producing  l)l(K)d.  The  same  end  might  have  been  attained  by  allow- 
ing the  hogs  which  were  to  be  vae(inate<l  to  associate  with  sick  hogs, 
but  owing  to  the  uncertainty  as  to  the  exact  time  when  infection 
would  take  j)lace  l)y  mere  association,  and  also  Ixnause  such  a  method 
would  not  ))e  suitable  for  practical  use,  the  blood-iujectioii  method  of 
infection  was  used  exclusively  in  the  ininumi/.jition  work. 

1'2H4()— No.  101.*— 08 «) 


82  PRODUCTION    OF    IMMUNITY   FROM    HOG    CHOLERA. 

It  will  be  understood,  however,  that  in  testing  the  curative  power 
of  a  serum  it  is  very  desirable  to  carry  out  the  experiments  with  ani- 
mals under  natural  conditions  as  nearly  as  possible.  For  this  reason, 
and  also  in  order  that  we  might  compare  results,  one  of  the  experi- 
ments to  test  the  curative  value  of  hyj)erimmune  serum  was  carried 
out  with  hogs  that  had  been  exposed  to  infection  by  association  sim- 
ply, wliile  in  the  other  experiments  hogs  that  had  been  infected 
through  disease-producing  blood  injections  were  used. 

In  this  connection  it  may  be  of  interest,  before  considering  the 
experiments  designed  to  test  the  curative  value  of  the  serum,  to  note 
the  results  of  a  single  experiment  wliich  was  designed  to  test  the  effect 
of  immediate  exposure  to  hog  cholera  by  association  with  sick  animals 
upon  hogs  that  had  been  injected  with  varying  sized  doses  of  immune 
serum. 

Experiment  XXVI. — Immediate  exposure  of  serum-treated  hogs  to  disease  by  association. 

Six  hogs  were  injected  subcutaneously  with  serum  from  immune 
1383;  two  received  5  c.  c,  two  10  c.  c,  and  two  15  c.  c.  of  the  serum. 
Immediately  after  injection  of  the  serum  all  were  placed  in  the 
Scribner  exposure  pen.  Two  checks,  not  treated,  were  placed  in  the 
same  pen  several  days  later,  as  shown  in  Table  29. 

Table  29. — Experiment  to  test  protective  value  of  1S83  serum  where  the  treated  animals 
icere  given  immediate  exposure  by  association. 


;                                                                          Exposure, 
hog       Weight.  I  Injected  Oct.  3,  190(3,  with-     


Date.        I  Result. 


Pounds.  ' 

1767. . . . 

50 

1768.... 

50 

1769.... 

40 

1770.... 

40 

1771.... 

45 

1772.... 

50 

1773.... 

50 

1774.... 

50 

5  c.  c.  serum Oct.     3, 1906     Remained  well 

do do Sickened  Oct.  10;  died 

j  Oct.  15,  1906. 

10  c.  c.  serum • do Remained  well 

do ' do do 

15  c.  e.  serum ' do do 

do do do 

Unvaccinated  check Oct.     8, 1906     Sickened    a  n  d    died 

Nov.  4,  190ti. 

do do I  Sickened    and    was 

1      killed  Oct.  18,  1906. 


Autopsy. 


Hemorrhage  s 
and  ulcers. 


llomorrha  g  ic 
lesions. 
Do. 


With  one  exception  (hog  1768,  injected  with  5  c.  c.  of  serum)  the 
hogs  that  received  serum  remained  well,  while  both  of  the  checks 
contracted  hog  cholera,  one  of  them  being  killed  to  secure  blood  for 
other  experiments.  This  experiment  should  be  considered  in  con- 
nection with  Experiment  XXVIII,  in  which  the  same  serum,  instead 
of  being  injected  simultaneously  with  the  exposure  to  disease,  was 
injected  at  varying  intervals  of  time  after  exposure  had  taken  place. 


CURATIVE   VALUE    OF    HYPERIMMUNE    SERUM. 


83 


S  S 


9.     9-     iiiilvi 
::    1      ?  =  -  7 

>  c  *  =  - 


H     =.      r-  = 


t«t££XUit£ 


2^2 


■r    --a.s-r-s-s 


o    •;,■=«- 


?      ?■  -^  J^    ■  l^' 


i   :c-: 
^  S  S  S  S  5  S  .^  S  S . 


i^  :2  .1^  Jr  .^  ,i 


:5  c 


L."^?. 


7^.  ' 


It  is  also  interest- 
ing to  compare  these 
results  with  those 
of  experiments  in 
which  the  s  a  m  e 
serum  was  used  in 
apj)roximately  the 
same  doses,  but  in 
which  the  simidtane- 
ous  exposure  to  dis- 
ease was  made  by 
injecting  disease- 
producing  blood. 
(See  Experiments 
V,  VI,  VII,  and 
VIII.) 

EXPERIMKNT    XXVII. — 

Curat ivr  value  of  Ncrum 
from  ho(j  l.iS-3;  exposure 
through  blood  inj e c- 
tions. 

Twelve  hogs 
weighing  50  pounds 
each  were  injected 
subcutaneously  with 
2  c.  c.  of  blood  from 
a  sick  hog  on  Sep- 
tember 29.  1900.  Of 
these  12  hogs,  2  were 
not  given  any  serum, 
but  were  lield  as 
controls  on  the  viru- 
lence of  the  diseased 
blood.  One  hog 
(1700)  was  not  in- 
ject^'d,  but  was 
placed  in  the  pen 
with  the  otheix  to 
(est  the  colitagioiis- 
ne.ss  of  the  disea.se. 

Two  (bjys  after 
infect  i  o  n  w  i  t  b 
d  i se  a se- producing 
l)lood  2  of  tbe 
infected    liogs   were 


84  PRODUCTION    OF    IMMUNITY    FROM    HOG    CHOLERA, 

injected  with  15  c.  c.  of  senim  each;  four  days  after  infection  2 
more  hogs  were  given  a  similar  dose  of  serum;  six  days  after  in- 
fection 4  more  of  the  infected  hogs  were  given  serum,  two  being 
given  30  c.  c.  each,  one  35  c.  c,  and  one  50  c.  c;  eight  days  after 
the  disease-producing  blood  was  administered  the  2  remaining  hogs 
of  the  10  reserved  for  treatment  were  given  50  c.  c.  each  of  serum. 
The  accompanying  table  (Table  30)  illustrates  very  well  the  method 
of  carrying  out  the  experiment  and  the  results  obtained.  The  2  hogs 
that  were  given  the  serum  two  days  after  injection  remained  per- 
fectly well;  those  that  were  first  given  serum  four  days  after  infection 
became  slightly  sick,  but  recovered.  The  hogs  that  were  given  serum 
on  the  sixth  and  eighth  days  after  infection  were  all  sick  when  treated, 
but  the  course  of  the  disease  was  apparently  not  affected  by  the  treat- 
ment, although  comparatively  large  doses  of  serum  were  used.  The 
same  serum,  however,  when  administered  simultaneously  with  disease- 
producing  blood  proved  effective  in  quite  small  doses  (5  c.  c. — See 
Experiments  V  and  VI).  The  2  hogs  (1762  and  1765)  that  were  not 
treated  with  serum  died  promptly,  as  was  to  be  expected,  and  the 
pen  check  also  contracted  disease  and  died.  The  4  surviving  hogs 
in  this  experiment  were  placed  in  the  Syphax  exposure  pen  a  few  days 
less  than  one  month  after  the  serum  injection;  all  survived  this 
exposure. 

If  conclusions  may  be  drawn  from  this  one  experiment,  we  would 
infer  that  even  very  large  doses  of  serum  will  not  save  hogs  when  it  is 
injected  more  than  four  days  after  infection,  but  that  prior  to  that 
time  much  smaller  doses  will  suffice. 

Experiment  XXVIII. — Curative  valueof  serinn  from  hog  1403;  exposure  by  association. 

Twelve  healthy  hogs,  weighing  approximately  60  pounds  each,  were 
placed  in  the  Scribner  exposure  pen  on  November  5,  1906.  One  day 
later  3  of  these  were  removed  from  the  exposure  pen  and  2  of  the  3 
were  given  20  c.  c.  each  of  serum,  the  third  hog  being  left  un- 
treated as  a  control.  This  procedure  was  repeated  three  times,  3  hogs 
being  removed  from  the  exposure  pen  on  the  second,  the  fourth,  and 
the  sixth  days  after  exposure.  In  each  instance  2  of  the  3  hogs  were 
injected  subcutaneously  with  20  c.  c.  of  serum  from  hog  1403. 

Table  31  shows  that  none  of  the  hogs  that  were  removed  from  tlie 
exposure  pen  within  forty-eight  hours  after  being  placed  there  showed 
any  signs  of  illness  as  a  result  of  that  exposure;  even  the  controls 
which  received  no  serum  remained  well.  Of  the  3  hogs  that  were 
taken  out  of  the  exposure  pen  four  days  after  exposure  all  became 
sick,  but  the  2  that  received  serum  recovered,  while  the  control  died. 
The  results  were  almost  precisely  similar  in  the  case  of  the  3  hogs  that 
were  removed  from  the  exposure  pen  six  days  after  having  been  placed 


CURATIVE   VALUE    OP    HYPERIMMUNE    SERUM. 


85 


5 


">. 


i  >  S  ~ 

=3  -  c 


a. 
s 


Q 


■5  I 


•c  ■-■^  ..  C£  a, 


•ao     > 


•;z 


z    ? 


z    fi 


— *  —  -^       MiMCI        "^        ^■V        -^        (C« 


2  — 

1 

c 

y. 

c 

c 

1 

c 

y 

c 

c 

c 

i 

0 

c 

c 

1   i 
i 

y. 

o 

^■  =  93     9?5     g     95      9      29 


o  —  ri    rt  ^  •-     c     I  -  <     w     a  • 

I-  r.  I.       |,i.(.       I.       i-t-       I-        JB  ; 
f.t.t.       JO  X,  *       jc       IT  r       r.       Z  ; 


there,  for  in  this  case  also 
the  2  serum-treated  hogs 
recovered  after  having 
been  somewhat  sick,  wliile 
the  untreated  control  died 
of  hog  cholera. 

In  summing  up  the  re- 
sults of  this  experiment, 
the  behavior  of  hogs  1870 
to  1875,  inclusive,  when 
later  exposed  to  infection, 
must  be  taken  into  consid- 
eration, for  the  deaths  of 
control  hogs  1872  and  1875 
as  a  result  of  tliis  second 
exposure  shows  that  they 
were  all  along  susceptible 
to  the  disease.  This  points 
strongly  to  the  likelihood 
that  none  of  the  first  6 
animals  in  this  experiment 
became  infected  from  the 
first  exposure  of  one  and 
two  days,  respectively,  in 
the  exposure  pen,  and  the 
immune  serum  can  not, 
therefore,  be  considered  as 
having  exerted  any  cur- 
ative influence  in  these 
cases,  although  its  immu- 
nizing action  is  well  shown 
by  the  exposure  of  Decem- 
ber 4, 1 906,  just  referred  to. 

The  hogs  tliat  were 
treated  with  serum  four 
days  and  six  days,  respec- 
tively, after  being  placed 
in  the  exposure  j)en  can 
not  be  regarded  as  liav- 
ing  become  infected  at 
once  after  being  placed  in 
the  exposure  pen,  for,  as 
shown  by  the  behavior  of 
the  contn)ls  in  the  lots 
tiiat  were  removed  on  tiie 


86  PRODUCTION    OF    IMMUNITY    FROM    HOG    CHOLERA. 

first  and  second  days,  infection  prol^ably  did  not  take  place  in  any 
of  the  hoojs  durinjj;  tlie  first  forty-eight  liours  in  the  exposure  pen. 
On  the  otlier  hand,  it  is  (^iiite  evident  from  the  behavior  of  hogs 
1876,  1877,  and  1878  that  infection  did  take  place  some  time  prior 
to  the  end  of  the  fourth  day  in  the  exposure  pen.  While  it  is  impos- 
sible, as  already  stated,  to  fix  the  time  of  infection  with  exactness, 
we  know  that  it  took  place  on  the  third  or  fourth  day.  It  is  plain, 
therefore,  that  the  serum  in  doses  of  20  c.  c.  saved  the  life  of  hogs 
that  had  been  infected  from  two  to  four  days  previously. 

DISCUSSION    OF    CURATIVE    ACTION    OF    IMMl'NE    SERUM. 

Earlier  experiments  have  shown  that  the  serum  from  hyperim- 
munized  immunes,  when  given  in  sufficient  dose,  may  be  expected 
to  protect  nonimmune  hogs  from  a  simultaneous  infection  with  hog 
cholera,  and  the  two  experiments  just  described  show  that  this  serum 
may  also  be  expected  to  prevent  the  death  of  hogs  when  it  is  admin- 
istered in  moderate  doses  within  four  days  after  infection  actually 
takes  place.  Later  than  this  it  is  probable  that  the  serum  in  virulent 
attacks  of  hog  cholera  will  do  little  good,  even  though  comparatively 
large  doses  are  given.  For  this  reason  it  seems  possible  that  serum 
from  immunes  prepared  in  the  maimer  described  in  this  paper  may 
not  prove  suitable  for  general  use  as  a  curative  agent  for  hog  cholera, 
although  in  cases  where  the  disease  is  recognized  soon  after  its  appear- 
ance in  a  herd  the  serum  would  probably  save  many  hogs  that  had 
been  exposed  only  a  few  days.  In  stating  that  the  serum  should  be 
administered  within  four  days  after  infection  to  insure  success,  we 
wish  to  make  it  plain  that  we  refer  to  the  date  of  actual  infection  and 
not  to  the  time  of  first  exposure,  for,  as  is  shown  by  Experiment 
XXVIII,  several  days  may  elapse  before  infection  takes  place  after 
exposure  to  disease  by  association,  (See  records  of  hogs  1872  and 
1875,  Experiment  XXVIII.) 

DTJHATION  OF  PROTECTIVE  POWER  IN  BLOOD  OF  IMMUNES,  AND 
KEEPING  QUALITY  OF  HYPERIMMUNE  SERUM. 

Tlie  original  plan  of  our  experiments  included  the  testing  of  serum 
drawn  from  the  immunes  at  different  periods  of  time  after  the  last 
injection  of  disease-producing  blood,  and  we  were  able  in  some  instances 
to  test  the  second  and  third  drawings  of  immune  serum,  but  as  these 
later  drawings  of  serum  were  apparently  quite  as  potent  as  the  first 
drawing,  the  ciuestion  of  the  duration  of  protective  power  in  the 
blood  of  the  immune  had  not  been  decided  by  the  experiments 
already  described.  For  the  purpose  of  testing  this  matter  still 
further  a  special  experiment  was  carried  out  with  a  drawing  of 
serum  from  immune  1234.  This  hog  furnished  part  of  the  serum 
used  in  the  1305  experiments,     (See  p.  11,) 


DURATION    OP    PROTECTIVE    POWER    OF    SERUM. 


87 


o      5 


-^     I 


S     w 


a    a 


c  r 


>      5 


ft       is        ~ 


OS  9/ 


■§>      »? 


£^     c|c~5 


r  c     «;  c< 


'  —  ^  $  ,^  — 


C    S,    —         G-   C  S 


■fx 


■ntotn 


^•* 


Experiment  XXIX.  —  Potency 
of  serum  draicn  seven  and  one- 
half  wonths  after  last  treatment 
of  immune. 

Tliis  experiment  practi- 
cally repeats  the  test  of  se- 
rum from  immune  1234 
that  was  carried  out  in 
1905.  Two  hogs  were  in- 
jected with  10  c.  c.  of  se- 
rum and  2  c.  c.  of  disease- 
producing  blood  each,  and 
2  with  20  c.  c.  of  serum  plus 
the  usual  dose  of  disease- 
producing  hlood;  at  the 
same  time  3  hogs  were  in- 
jected with  2  c.  c.  each  of 
disease  -  producing  blood 
alone,  and  1  healthy  hog 
was  placed  in  the  pen  with 
these  in  order  to  make  sure 
of  the  infectiousness  of  the 
disease. 

Table  32  shows  the  man- 
ner of  carrying  out  this 
experiment  as  well  a^s  the 
results  obtained.  The  sig- 
nificance of  the  experiment 
may  })erha|)sl)ebest  ap})re- 
ciated  by  a  comparison  of 
the  action  of  serum  from 
the  same  hog  <lrawn  nearly 
a  year  before,  shortly  after 
an  injection  of  disease-pro- 
ducing blood.  The  action 
of  blood  from  nonliy])er- 
iinmunized  iinmunes,  as 
shown  in  Kxperinients  XX 
an<l  XXI,  slionld  also  be 
kept  in  mind. 

'i'able  32  shows  that  all 
of  the  vacciinUed  hogs  be- 
cauje  sick  as  a  result  of  tho 
treatment,  but  they  all  re- 
covered.   TIm'  3  hogs  (  H»(')l , 


88  PRODUCTION    OF    IMMUNITY   FROM    HOG    CHOLERA. 

1662,  and  1663)  that  received  the  same  dose  of  the  same  disease-pro- 
ducing blood  alone  likewise  became  sick  and  all  died,  and  they  com- 
municated the  disease  to  their  pen  check. 

The  vaccinated  hogs  were  exposed  to  hog  cholera  during  the  pas- 
ture outbreak  about  six  weeks  after  vaccination.  They  all  remained 
well  and  when  placed  in  the  Scribner  exposure  pen  three  months  and 
nineteen  days  after  vaccination  were  still  completely  immune  to  the 
disease. 

Inasmuch  as  10  c.  c.  and  20  c.  c.  of  serum  drawn  from  immune  1234 
in  1905  gave  complete  protection  from  a  fatal  dose  of  disease-pro- 
ducing blood,  and  as  the  last  drawing,  made  seven  and  one-half 
months  after  the  last  treatment  with  disease-producing  blood,  gave 
only  partial  protection  (the  serum  in  this  case  prevented  death,  but 
did  not  prevent  illness),  we  may  conclude  that  the  protective  power  of 
the  blood  of  immune  1234  had  diminished  somewhat  seven  and  one- 
half  months  after  the  last  disease-producing  blood  injection.  But 
although  the  potency  was  diminished,  it  was  still  present  in  a  marked 
degree,  and  although,  owing  to  the  limited  number  of  tests  that  have 
been  made,  we  can  not  be  absolutely  certain,  it  is  at  least  reasonable 
to  believe  that  this  power  was  due  to  the  previous  injections  of  disease- 
producing  blood  and  not  to  a  natural  protective  power  existing  nor- 
mally in  the  blood  of  the  immune.  (See  experiments  with  blood  from 
nonhyperimmunized  immunes,  p.  71.)  This  question  is  one  of  prac- 
tical importance,  and  further  experiments  along  this  line  will  be  car- 
ried out. 

Experiment  XXX. —  The  keeping  quality  of  immune  serum. 

A  quantity  of  hyperimmune  serum  prepared  in  1905  remained 
Unused  in  the  experiments  of  that  year,  and  as  it  was  very  desirable 
to  know  how  long  the  serum,  prepared  with  carbolic  acid,  would  retain 
its  potency,  we  have  utilized  some  of  this  1905 -serum  in  experiments 
designed  to  test  this  point. 

The  serum  used  was  from  1905  immunes  Q  No.  2  and  1234,  and  was 
drawn  from  these  hogs  on  December  1,  1905,  and  November  21,  1905, 
respectively.  Immediately  after  being  drawn  these  sera  were 
mixed  with  a  5  per  cent  solution  of  carbolic  acid  in  such  proportion 
that  the  serum  contained  0.5  per  cent  carbolic  acid.  After  the 
addition  of  this  preservative  the  serum  was  placed  in  sterilized  bottles 
and  kept  in  a  cool  place  until  June  6,  1906,  when  it  was  used  in  the 
following  experiment. 

Two  hogs,  W  1925  and  W  1926,  were  injected  subcutaneously 
with  5  c.  c.  of  Scribner  disease-producing  blood,  and  at  the  same 
time  hog  W  1925  was  given  20  c.  c.  and  hog  W  1926  was  given  17 
c.  c.  of  hyperimmune  serum  from  hog  1234.  Hogs  W  1928  and  W 
1929  were  given  5  c.  c.  each  of  the  same  disease-producing  blood,  but 


KEEPING   QUALITY   OP   SERUM. 


89 


'S* 


3     s 


s       y 


5  o'S 

**£  5 

M      si 


M     05 


S        t-- 


r:     -o     ~     "■= 


liii 


c_c      c    .  r — 


«^2 


i  I 

•3    5    ""    — 

'^  bo'-''  6*ff, 

«  ^  ^  =  ^ 

e-S  i  c  t- 

S    '-    i 


or:    '  c 


!J^     ?,     \r,     ?!     ?,a     5     i-' 


wo 


<.5 


4)   O 

Si  u. 

eg 
■HP. 


c  c 


received  20  c.  c.  each  of  hyper- 
immune senim  from  immune 
QNo.  2.  An  untreated  hog  was 
placed  in  each  of  the  two  pens 
w4th  the  vaccinated  hogs.  As 
controls,  2  hogs  (W  1931  and 
W  1932)  were  each  given  5  c.c. 
of  the  same  disease -producing 
blood  as  was  used  for  injecting 
the  4  senim-treated  hogs.  These 

2  hogs  were  placed  in  a  sepa- 
rate pen. 

As  may  be  seen  from  Table 
33,  none  of  the  4  hogs  that  re- 
ceived the  simultaneous  injec- 
tions of  serum  and  disease-pro- 
ducing blood  showed  any  symp- 
toms of  illness  after  injection, 
while  both  of  the  hogs  that  were 
given  the  disease  -  producing 
blood  alone  sickened  and  died  of 
hog  cholera.  The  4  vaccinated 
hogs,  with  their  2  pen  checks, 
were  exposed  to  hog  cholera 
about  seven  weeks  after  vacci- 
nation. As  a  result  of  this  ex- 
posure, both  check  animals  died 
of  hog  cholera,  while  1  of  the 
vaccinated  hogs  became  slightly 
sick,  but  soon  recovered.     The 

3  other  vaccinated  liogs  did  not 
show  any  signs  of  ilhiess. 

This  expcriincnt  shows  that 
hyperinununc  scrum  preserved 
with  carbohc  acid  nuiy  retain  its 
potency  for  at  least  six  months. 

GENERAL  SUMMARY    OF  RE- 
SULTS. 

In  the  cx|)crimcnts  of  1905 
and  190»),  \'\  immune  hogs  (in- 
cluding hog  MOD  were  used  ft)r 
the  pnxliiction  of  scrum,  and 
all  of  these,  with  one  exception 


90  PRODUCTION    OF    IMMUNITY   FROM    HOG   CHOLERA. 

(immune  Q  No.  I,  1905),  after  hyperimmunization  have  furnished 
serum  that  in  doses  of  15  c.  c.  or  more  gave  protection  from  a 
simultaneous  injection  of  disease-producing  blood.  Wlien  smaller 
doses  of  serum  were  given,  differences  in  the  potency  of  the  various 
sera  could  be  observed.  The  doses  of  immune  serum  given  with 
disease-producing  blood  varied  from  2 J  to  20  c.  c,  and,  as  was  to 
be  expected,  some  of  the  hogs  that  received  the  smaller  doses  were 
not  sufficiently  protected.  In  summarizing  the  results  of  these 
experiments,  therefore,  the  percentage  of  loss  which  resulted  from 
vaccination  is  not  to  be  regarded  as  representing  what  would  occur 
in  the  practical  application  of  the  method,  for,  as  already  stated, 
when  a  sufficient  dose  of  serum  is  used  no  deaths  are  caused  by  the 
immunizing  treatment.  Even  though,  for  the  reasons  just  stated, 
the  average  results  of  our  experiments  are  not  to  be  considered  as 
representing  what  should  be  obtained  in  practice,  a  summary  of  these 
results  is  not  without  interest  as  showing  in  a  general  way  the  beha- 
vior of  serum-treated  hogs  as  compared  with  unprotected  hogs  when 
both  are  exposed  to  disease  through  injections  of  disease-producing 
blood. 

In  all,  168  hogs  were  given  a  simultaneous  injection  of  serum  and 
disease-producing  blood,  the  dose  of  serum  varying  from  2^  c.  c.  to 
20  c.  c.  Of  these,  35,  or  21  per  cent,  showed  visible  symptoms  of 
illness  after  injection,  and  15,  or  approximately  9  per  cent  of  the  total 
number,  died.  As  a  contrast  to  this  we  find  that  54  hogs,  were 
injected  with  the  same  dose  of  the  same  disease-producing  blood 
alone.  Of  these,  54,  or  100  per  cent,  became  sick,  and  50,  or  92.5 
per  cent,  died  of  hog  cholera.  These  figures,  we  believe,  show  beyond 
doubt  that  by  hyperimmunizing  immunes  in  the  manner  described 
in  this  paper  a  highly  potent  serum  may  be  secured.  We  are  con- 
fident also,  as  a  result  of  the  experiments  we  have  described,  that 
had  we  used  the  larger  doses  of  serum  in  all  cases  or  else  reduced 
the  dose  of  disease-producing  blood  the  percentage  of  deaths  follow- 
ing vaccination  would  have  been  so  small  as  to  be  without  practical 
significance. 

TRANSMISSION  OF    DISEASE    BY   HOGS   TREATED  BY    SERUM- 
SIMULTANEOUS  METHOD. 

To  test  the  possibility  of  disease  being  conveyed  to  normal  hogs 
by  hogs  that  had  been  vaccinated,  58  shoats  were  placed  in  the  pens 
with  the  vaccinated  hogs.  Of  these  pen  checks  none  became  sick 
unless  some  of  the  vaccinated  hogs  with  which  they  associated 
became  severely  ill;  indeed  in  a  number  of  instances  the  pen  checks 
remained  well,  even  though  they  associated  with  vaccinated  hogs 
exhibiting  undoubted  symptoms  of  hog  cholera.  From  this  it  appears 
that  the  immune  serum  not  only  possesses  the  power  to  protect  hogs 


DISCUSSION    OF    RESULTS    OF    EXPERIMENTS.  91 

from  a  simultaneous  injection  of  disease-producing  blood,  but  that 
even  in  cases  where  too  little  serum  is  given  it  yet  has  a  marked  ten- 
dency to  lessen  the  infectiousness  of  the  disease.  Of  the  58  pen  checks 
exposed  to  vaccinated  hogs,  6  contracted  hog  cholera  and  5  died. 

As  a  control  experiment,  19  shoats  were  placed  in  the  pens  with  the 
hogs  that  were  injected  Anth  disease-producing  blood  alone.  Of 
these,  all  became  sick,  17  died,  1  was  killed  to  secure  blood  for  other 
experiments,  and  1  recovered.  In  other  w^ords,  of  the  pen  checks 
exposed  to  hogs  injected  with  disease-producing  blood  alone,  94  per 
cent  died,  whereas  only  8  per  cent  of  the  checks  exposed  to  vacci- 
nated hogs  succumbed. 

IMMUNITY  IN  HOGS  AFTER  SERUM-SIMTJLTANEOTTS  VACCINATION. 

In  describing  the  individual  experiments  attention  has  been  called 
to  the  accidental  exposure  to  hog  cholera  of  those  vaccinated  hogs 
that  were  being  reserved  for  a  late  exposure  in  order  to  test  the  dura- 
tion of  the  immunity  conferred  by  the  serum-simultaneous  and  the 
serum-alone  methods.  The  pasture  in  which  this  accidental  outbreak 
of  disease  occurred  contained  a  large  number  of  hogs  which  had  been 
treated  at  different  times,  and  as  a  consequence  this  exposure  took 
place  only  a  few  weeks  after  vaccination  in  the  case  of  some  of  the  hogs, 
while  in  the  case  of  others  the  interval  between  vaccination  and  expo- 
sure was  as  great  as  three  montlis.  Aside  from  the  hogs  that  were  acci- 
dentally exposed  in  this  way,  a  considerable  number  were  placed  in 
the  exposure  pen  within  tlu*ee  weeks  after  vaccination,  tlie  object 
being  to  compare  the  immunity  at  this  time  with  that  exhibited  by 
others  treated  in  the  same  way  but  exposed  very  much  later.  For  the 
reasons  given,  this  comparison  could  not  be  made  iu  all  cases,  and  all 
results  of  exposure  to  hog  cholera  are  therefore  considered  togc^ther  in 
this  summary,  it  being  understood  that  ex])osurG  took  ])lace  from  three 
weeks  to  three  months  after  vaccination. 

Of  the  hogs  treated  by  the  .senim-sinudtaneous  method,  ]'M]  were 
exposed  to  hog  cholera,  and  4,  or  nearly  '.i  per  cent,  died  as  a  result, 
while  of  68  imvaccinated  hogs  ex})osed  under  the  same  conditions,  .")(), 
or  approximately  82  per  cent,  died. 

In  regard  to  the  4  vaccinated  hogs  that  are  stated  to  have  died  from 
exposure  after  vaccination,  it  should  be  n<tte(l  that  there  is  room  for 
ctmsiderable  doubt  as  to  the  cause  of  death.  In  only  one  of  these  hogs 
(1780)  were  typical  lesions  of  hog  cholera  found  at  autop.sy;  and  as 
this  hog  remained  unthrifty  after  vaccinatit)n.  and  as  its  mate  (17S1) 
treated  in  the  same  niann<>r  died  from  vaccination,  it  is  not  unlikely 
that  the  intestinal  lesions  found  at  the  autopsy  of  hog  17S(>  resulted 
from  vaccination  and  not  from  exposure.  N»Mther  of  the  other  three 
hogs  exhibited  lesions  of  hog  cholera  at  autopsy,  and  two  of  them 
(l.^^'J  and  ir)r)(i)  ])as.sed  through  exj)osure  iji  the  j)astMn'  and  only  sue- 


92  PRODUCTION   OF   IMMUNITY  FROM   HOG  CHOLERA. 

Climbed  when  placed  in  the  exposure  pen.  The  conditions  in  this  ex- 
posure pen  were  not  conducive  to  thriftiness,  for  no  attempt  was  made 
to  disinfect  or  clean  the  pen,  as  this  might  have  defeated  its  object, 
which  was  to  furnish  a  certain  and  severe  exposure  to  hog  cholera. 
Before  leaving  this  subject,  we  wish  to  state  our  conviction  that  as 
small  as  was  the  loss  among  vaccinated  hogs  exposed  to  hog  cholera, 
this  would  have  been  even  less  had  the  exposure  taken  place  under  the 
conditions  usually  met  with  in  practice. 

IMMUNITY  IN  HOGS  TREATED  WITH  SERUM  ALONE. 

In  all,  58  hogs  were  treated  with  serum  alone  in  the  experiments 
of  1906.  None  of  these  showed  any  ill  effects  from  the  treatment, 
and  49  were  subsequently  exposed  to  hog  cholera.  Of  these,  23,  or 
47  per  cent,  survived  exposure,  whereas  of  68  untreated  hogs  which 
served  as  controls  only  18  per  cent  survived.  It  is  thus  evident  that 
the  protection  afforded  by  the  hyperimmune  serum  when  given 
alone,  while  it  did  not  equal  that  afforded  by  the  serum-simultaneous 
method,  was  nevertheless  sufficient  to  protect  nearly  50  per  cent  of 
the  treated  animals  against  subsequent  exposure. 

As  regards  the  duration  of  the  protection  afforded  by  the  serum 
when  given  alone,  we  find  that  of  49  animals  treated  with  serum 
alone,  26  were  exposed  within  three  weeks  after  receiving  the  serum, 
and  23  were  exposed  after  one  to  three  and  one-half  months.  Of 
the  first  lot,  exposed  within  three  weeks,  9,  or  34.6  per  cent,  died  as 
a  result  of  the  exposure,  while  of  the  23  exposed  after  one  to  three 
and  one-half  months,  17,  or  73  per  cent,  succumbed.  From  these 
results  it  would  seem  that  the  protection  afforded  by  the  serum  when 
administered  alone  is  not  as  lasting  as  when  administered  in  combi- 
nation with  diseased  blood. 

CURATIVE  VALUE  OF  HYPERIMMUNE  SERUM. 

The  exact  methods  of  carrying  out  the  experiments  has  been  de- 
scribed elsewhere.  Twelve  hogs  that  were  certainly  infected  with 
hog  cholera  were  treated  with  serum  after  the  elapse  of  different 
lengths  of  time,  and  the  results  showed  that  doses  of  15  or  20  c.  c. 
were  sufficient  to  save  the  life  of  the  treated  hogs,  provided  the  serum 
was  given  within  four  days  after  the  date  of  infection.  If  given 
later  than  this,  even  much  larger  doses  (35  to  50  c.  c.)  were  not  suffi- 
cient to  save  the  infected  hogs  from  the  severe  exposure  to  which  they 
were  subjected. 


DISCUSSION    OF    RESULTS    OF    EXPERIMENTS.  •  93 

RESULTS  WITH  SERUM  FROM  IMMUNES  TREATED  BY  DIFFERENT 
METHODS  WITH  DIFFERENT  DISEASE-PRODUCING  BLOODS. 

In  the  previous  summaries  simply  the  general  results  have  been 
considered,  without  reference  to  any  differences  that  may  have  been 
found  in  the  action  of  serum  prepared  by  the  different  methods  or  by 
the  use  of  different  strains  of  disease-producing  blood,  and  also  with- 
out regard  to  differences  in  the  immunes  themselves.  In  discussing 
these  features  we  wish  to  call  attention  again  to  the  fact  that  the 
figures  given  are  not  to  be  taken  as  representing  what  may  be  ex- 
pected in  actual  practice,  for  it  is  probable  that  all  of  the  serum 
would  have  given  better  results  if  the  doses  had  been  somewhat  larger 
in  certain  cases. 

COMPARISON     OF     THE     QUICK     AND     SLOW     METHODS     OF     PRODUCING 
HYPERIMMUNE    SERUM. 

The  comparative  potency  of  the  sera  prepared  by  the  quick  and 
slow  methods  may  no  doubt  be  best  shown  by  comparing  the  results 
obtained  by  injecting  nonimmune  hogs  simultaneously  with  serum 
and  a  fatal  dose  of  disease-producing  blood.  In  the  experiments  of 
1905  and  1906,  86  hogs"  were  treated  in  this  way  with  serum  pre- 
pared by  the  quick  method.  Of  these  86  hogs,  7,  or  approximately  8 
per  cent,  died  from  the  injection.  There  were  treated  with  serum 
prepared  by  the  slow  method  82  hogs,  all  of  which  were  injected  at 
the  same  time  with  disease-producing  blood.  Of  these,  nearly  10  per 
cent  died  as  a  result  of  the  injection.  The  slight  difference  in  favor 
of  the  quick  method  we  are  inclined  to  attribute  to  other  causes  than 
to  the  method  used  for  producing  the  serum,  and  it  seems  ])robable 
that  one  method  will  be  found  as  suitable  as  the  other  for  producing 
a  potent  serum,  though  of  course  in  either  case  the  potency  might 
be  heightened  by  increa.sing  the  dose  of  disease-producing  blood 
given  the  immune.  The  potency  of  the  seriun  secured  being  e(jual, 
the  ciuick  method  would  probably  be  found  more  desirable  for  prac- 
tical use. 

THE    COMPARATIVE    POTENCY    OF    SEHA    SECIKKD    BY    11 Y PKHIMMUNIZ.V- 
TION     WITH    THE    SCRIBNEK    AND    SYPHAX    STRAINS    OK    DISEASE. 

Senim  from  8  hogs  was  used.  4  having  been  l)y|)eriinnuinized  with 
Scribner  disease-j)roducing  blood,  and  4  with  Svphax  i)lood.  In  all, 
74  hogs  were  treated  with  s<'nnn  from  tlie  S<  ribncr  iinnmnes  at  the 
same  time  that  they  were  injected  with  disease-producing  blood;  a.s 
a  result,  4,  or  appn>xiniately  .')l  |)er  cent.  iVwd.  In  the  case  of  the 
serum  from  the  Svphax  iniiinines.  72  hogs  were  given  <iisease- 
producing  blood  siMiiihaneonsly  with  serum,  and.  as  a  result ,  S,  or  1 1 


flThb*  inchidc.'*  the  hi>g.«  ircatcd  with  ^'<•rum  Irom  iinimiiic  IIOI. 


94  PRODUCTION    OF    IMMUNITY    FROM    HOG    CHOLERA. 

per  cent,  died.  The  apparent  lower  potency  of  the  Syphax  hyper- 
immune serum  is  caused  by  the  distinctly  weaker  power  of  the  serum 
from  1  hog  (1310),  a  dose  of  10  c.  c.  of  this  serum  being  too  small 
to  protect  nonimmunes,  although  larger  doses  were  entirely  satis- 
factory. Inasjnuch  as  the  average  potency  of  the  serum  from  the 
other  3  immunes  hyperimmunized  with  the  Syphax  blood  was 
quite  as  great  as  that  of  those  treated  with  the  Scribner  blood,  we 
are  inclined  to  believe  that  the  lower  potency  of  serum  from  hog 
1310  was  due  to  some  peculiaritj^  of  this  hog  and  not  to  a  lower 
hyperimmunizing  power  of  the  Syphax  blood. 

COMPARATIVE    POTENCY    OF    SERA    FROM    HOGS    POSSESSING    NATURAL 
IMMUNITY   AND   FROM  THOSE   POSSESSING  ACQUIRED   IMMUNITY. 

Attention  has  already  been  directed  to  the  difficulty  experienced  in 
deciding  whether  a  particular  animal  should  be  classed  as  one  possess- 
ing acquired  immunity  or  natural  immunity.  In  fact  the  whole  ques- 
tion seems  to  be  simply  one  of  degree  of  resisting  power  on  the  part  of 
the  hog.  In  any  outbreak  of  hog  cholera  it  is  probable  that  at  least 
a  few  hogs  will  survive.  Some  of  these  may  have  been  markedly 
sick  and  have  recovered  only  after  a  long  siege  of  the  disease,  while 
others  may  have  been  only  slightly  indisposed,  and  still  others  may 
not  have  exhibited  visible  symptoms  of  disease.  It  seems  hardly  cor- 
rect to  speak  thereafter  of  one  of  these  hogs  as  a  natural  immune,  and 
to  regard  another  as  having  acquired  immunity  through  the  attack  of 
disease.  We  are  rather  inclined,  in  the  light  of  our  present  knowledge 
of  the  disease,  to  regard  all  hogs  as  being  naturally  susceptible  but 
varying  greatly  in  the  degree  of  resisting  power  which  they  possess. 
If  this  assumption  be  correct,  it  would  be  expected  that  a  protective 
serum  might  be  obtained  by  the  hjrperimmunization  of  any  immune 
hog,  the  differences  in  the  serum  from  different  hogs  being  simply  in 
degree  of  potency  and  depending  probably  upon  the  intensity  of  the 
reaction  produced  by  the  injection  of  diseased  blood. 

In  actual  practice  we  have  been  able  to  secure  but  one  immune  that 
had  actually  been  sick  of  hog  cholera  that  was  vigorous  and  suitable 
for  hyperimmunization.  The  serum  from  this  immune  (1392),  as  the 
records  show,  is  not  more  potent  than  that  obtained  by  similar  meth- 
ods of  hyperimmunization  from  other  hogs  that  had  never  shown 
visible  symptoms  of  illness  when  exposed  to  hog  cholera.  In  fact  the 
sera  from  the  different  immunes,  with  the  exception  of  hogsQ  No.  2 
and  No.  1310,  were  quite  uniform  in  potency.  The  lesser  potency  of 
the  sera  from  the  two  hogs  just  mentioned  can  not  be  explained  upon 
the  ground  of  natural  immunity,  but  probably  was  caused  by  some 
individual  peculiarity  which  we  do  not  understand. 


CONCLUSIONS.  95 

The  remaining  experiments,  not  mentioned  in  this  general  summary, 
have  already  been  discussed  at  some  length  and  it  seems  unnecessary 
to  refer  to  them  further  at  this  time.  Before  closing  this  discussion, 
however,  we  wish  to  suggest  to  anyone  who  may  have  occasion  to 
repeat  these  experiments  that  it  is  essential  to  make  sure  that  the 
outbreak  from  which  blood  is  secured  for  hyperimmunization  exhil)- 
its  all  of  the  characteristics  of  hog  cholera"  and  likewise  that  the 
blood  used  in  conjunction  ^^^th  the  serum  for  serum-sinmltaneous 
vaccination  is  taken  from  a  hog  suffering  from  undoubted  hog 
cholera.  In  addition,  more  than  one  hog  should  be  liA-perimmunized 
in  order  that  individual  peculiarity  on  the  part  of  one  hog  may  not  lead 
to  erroneous  conclusions.  As  the  methods  herein  described  involve 
the  use  of  a  disease-producing  virus  we  believe  that  onh'  those  trained 
in  bacteriological  methods  should  attempt  to  use  them,  and  in  all  cases 
before  the  serum  is  employed  in  a  practical  way  the  amoimt  retpiired 
to  give  protection  from  a  fatal  dose  of  disease-producing  blood 
should  be  determined  experimentally. 

CONCLUSIONS. 

(1)  When  hogs  immune  from  hog  cholera  are  injected  with  suitable 
amounts  of  vinilent  blood  taken  from  hogs  sick  of  hog  cholera  the 
blood  serum  of  the  immunes  acquires  the  power  to  protect  nonim- 
mune hogs  from  an  otherwise  fatal  dose  of  disease-producing  blood 
administered  simultaneously  with  the  serum. 

(2)  Immunes  which  have  never  exhibited  s\nnptoms  of  disease 
after  exposure  to  hog  cholera  (natural  immunity)  nuiy  furnish 
equally  as  potent  serum  as  those  whicii  have  recovered  from  an  at- 
tack of  the  disease  (acquired  imnumity). 

i'.i)  Ilj'perimnuuiization  may  be  accomplished  equally  as  well  by 
the  administration  of  one  large  dose  of  (lisea.se-produciug  blood  us  by 
repeated  injections  of  smaller  doses. 

(4)  Ilyperinnnunization  may  be  accoiuplished  with  blood  from 
any  virulent  strain  of  hog  cholera. 

(.5)  Ilyperinumniized  hogs  j)r()bably  retain  for  several  mouths  tlu^ 
j)ower  to  furnish  a  ])otent  senim. 

(())  Serum  from  properly  hyperiuuiniuized  hogs  iu  doses  t)f  JO  «■.  c. 
should  protect  nonimmunes  weighing  from  _'.")  to  .")()  pounds  from  a 
fatal  <iose  of  di.sea.se-pr<)ducing  blood  administered  sinudlaneously. 

(7)  Imnumity  in  hogs  treat<'d  by  the  .s(>ruin-siundtaJU'ous  method 
lasts  at  least  three  and  one-half  months  and  probahly  l<»ng«'r. 

(H)  In  serum-simultaneous  vaccination  it  is  not  necessary  to  pro- 
duce illness  in  the  vaccimited  hog  in  ohNt  to  secure  nn  iuuuunity 
lastingforat  least  three  months. 

"See  JJullolin  7J,  IJuniiu  i>l  Animal  Iii<liistr\ .  p.  iL'. 


96  PRODUCTION    OF    IMMUNITY    FROM    HOG    CHOLERA. 

(9)  If  a  suincieiit  dose  of  serum  is  given,  hogs  are  not  injured  by 
the  serum-simultaneous  vaccination. 

(10)  Hogs  vaccinated  by  the  serum-simultaneous  method  do  not 
communicate  disease  to  others  unless  they  themselves  become  sick. 

(11)  Serum  administered  alone  may  not  furnish  complete  protec- 
tion for  a  longer  period  than  three  weeks. 

(12)  The  serum  probably  can  be  used  successfully  as  a  curative 
agent  if  administered  in  the  eariy  stages  of  the  disease. 


O 


